FORM 6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16
of the Securities Exchange Act of 1934

For the month of December, 2004

Commission File Number 1-7616

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

Form 20-F þ                    Form 40-F o

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):_________

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):_________

Indicate by check mark whether by furnishing the information contained in this Form, the registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes o                    No þ

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-_________

Table of Contents

SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

This report on Form 6-K contains the followings:

(TRANSLATION)

THE 59TH SEMIANNUAL BUSINESS REPORT
For the Six Months Ended September 30, 2004

This is a translation of the original Semiannual Business Report written in the
Japanese language, prepared primarily for the benefit and information
of shareholders of the Company’s common stock.

PIONEER CORPORATION
Tokyo, Japan

TO OUR SHAREHOLDERS

In the first half of the 59th accounting period, ended September 30, 2004, consolidated operating revenue of Pioneer Corporation was ¥345,047 million, rising 7.8% over the previous year.

Operating income decreased 24.4% from the corresponding period of the previous year to ¥13,273 million. This decrease occurred despite increased net sales, and reflected a decreased gross profit margin due to intensified price competition for our major products and decreased profit from patent licensing as a result of a decline in royalty revenue. Net income came to ¥4,809 million, a 61.5% decrease, due to a decrease in operating income as well as absence of the ¥4,639 million income from discontinued operations recorded in the corresponding period of last year as a result of the sale of subsidiaries in the audio/video software business.

Interim dividend payments were set at ¥12.5 per share of common stock, the same amount as last year.

The business environment remains severe, characterized by uncertain economic conditions in our major markets, Japan, North America and Europe, price competition beyond our projections in our major product categories, and exchange rate fluctuations. In order to achieve the medium-term management plan, the Company is concentrating resources on strategic businesses as described below to recover profits and improve efficiency.

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In our plasma display business, we are working to build up capacity of the production system to meet fast-growing demand, thereby increasing profitability of the business. Our recently added fourth line has expanded our production capacity to approximately 600,000 units a year. Our new plant, acquired from NEC Corporation in September 2004, further increased Pioneer’s plasma display production capacity, bringing it to a total of approximately 1,100,000 units a year.

In the DVD business, markets for DVD recorders, especially those with large-capacity hard disk drives (HDDs), and recordable DVD drives for personal computers (PCs), are rapidly growing. On the other hand, price competition is getting harsher. To cope with the situation, we are advancing cost cutting by, for example, carrying out integrated production from laser pickups to finished products in China. We are also expanding sales of drive units for DVD recorders to other manufacturers.

In our car electronics business, we continue our efforts to strengthen our leadership in the consumer and OEM (original equipment manufacturing) markets. Our car navigation systems enjoy an excellent reputation in Japan, and we intend to expand this business in Europe and North America. In the car audio business, we plan to fortify our strong position with distinctive new products, and maintain earnest sales efforts in such growing markets as China and Central and South America.

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We will continue to minimize operating costs and expenses worldwide. We are expanding production in China to reduce overall manufacturing costs; implementing an expense supervision system to lower the ratio of our selling, general and administrative expenses to consolidated operating revenue; and applying supply chain management to review and optimize inventory control worldwide, for everything from parts procurement to retailer supply, on a weekly basis. We believe that such initiatives will help us return to growth in profitability and improve cash flows.

We sincerely hope that you, our shareholders, will continue in your understanding and support of Pioneer.

December 2004
Tokyo, Japan

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CONSOLIDATED OPERATING REVENUE BY BUSINESS SEGMENT

At the year end of fiscal 2004, the Company changed business segment classification for certain businesses. Results related to recordable DVD drives have been moved from “Others” to “Home Electronics,” and results related to plasma displays for business use have been moved from “Home Electronics” to “Others.” Corresponding figures of the previous periods have been reclassified accordingly.

Percent of Operating Revenue

Home Electronics

This segment includes DVD players, DVD recorders, recordable DVD drives, DVD-ROM drives, home-use plasma displays, projection TVs, stereo systems, individual stereo components, equipment for cable-TV systems, digital broadcast set-top boxes and telephones.

Sales in the Home Electronics segment increased 4.6% to ¥123,684 million from the corresponding period last year. In Japan, sales rose 9.1% to ¥35,664 million primarily due to a large increase in sales of home-use plasma displays and DVD recorders, despite the decreased sales of recordable DVD drives for PCs. Overseas sales increased 2.8%

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to ¥88,020 million in the corresponding period last year, reflecting an increase in sales of home-use plasma displays and DVD recorders worldwide, despite a decline in sales of recordable DVD drives and audio products worldwide.

Car Electronics

This segment includes car stereos, car AV (audio/video) systems, car speakers and car navigation systems.

Sales in the Car Electronics segment amounted to ¥154,325 million, up 8.8% over the corresponding period in the previous year. In Japan, sales increased 8.2% to ¥61,784 million, reflecting increased car navigation system sales to automobile manufacturers, despite decreased sales of such systems to the consumer market. Overseas sales increased 9.2% to ¥92,541 million, primarily due to higher sales of car navigation systems in North America and Europe, audio products to automobile manufacturers in North America and car audio products in Asia and Central and South America.

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Patent Licensing

This segment includes the licensing of patents related to optical disc technologies.

Royalty revenue from Patent Licensing decreased 19.8% from the corresponding period in the previous year to ¥6,739 million. This was due to a decline in royalty revenue resulting from the expiration of the Company’s optical disc-related patents in certain areas.

Others

This segment includes business-use plasma displays, business-use AV systems, organic light-emitting diode (OLED) display panels, factory automation (FA) systems, and devices and parts.

Sales in this segment increased 17.2% from the corresponding period in the previous year to ¥60,299 million. In Japan, sales were lower by 3.5%, at ¥26,535 million primarily due to a decrease in sales of OLED display panels and a sales shift from Japan to China of semiconductors related to laser pickups, despite the increase in sales of FA systems. Overseas, sales were up 40.9% over the previous year to ¥33,764 million, primarily due to increased sales of devices for cellular phones and semiconductors related to laser pickups in China, as well as FA systems in Asia, despite decreased sales in North America and Europe of business-use plasma displays.

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CONSOLIDATED FINANCIAL STATEMENTS
Pioneer Corporation and Subsidiaries

(1) Consolidated Balance Sheets

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(2) Consolidated Statements of Income

(In millions of yen except per share information)

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(3) Consolidated Statements of Cash Flows

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Notes:

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NON-CONSOLIDATED FINANCIAL STATEMENTS
Pioneer Corporation — Parent Company Only

(1) Condensed Balance Sheets

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(2) Condensed Statements of Income

Notes:

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CONDITION OF SHAREHOLDERS AND SHARES
(as of September 30, 2004)

Note: 4,631,332 shares of treasury stock held by the Company are included.

Distribution of Share-ownership

Note: Japanese individuals and others include 4,631 thousand shares as treasury stock held by the Company.

Top Ten Largest Shareholders

Note: The Company holds 4,631 thousand shares as treasury stock.

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Price per Share and Volume of Shares Traded on the Tokyo Stock Exchange

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