Shares in Apple fell 6.4% on Tuesday after long-standing market rumours were confirmed when it unveiled a low-cost computer at the annual MacWorld event.
Investors had been speculating ahead of the Mac Mini launch
Its stock had doubled since September, amid new product speculation and the success of the iPod music player.
"I think it was a case of buy on the rumour and sell on the news," said Marc Pado, strategist at Cantor Fitzgerald.
Investor sentiment was also dented by iPod sales, which were strong but below the hopes of some Wall Street analysts.
Apple revealed it had sold 4.5 million iPods in the last quarter of 2004, which includes the important festive season.
Chief executive Steve Jobs also unveiled a cheaper and smaller music player at MacWorld in San Francisco.
Industry observers said the new music player will help Apple as its faces competition in the digital music player market from the likes of Sony, Creative and Rio.
"Offering these lower-priced players allows Apple to attract not just new users but those who already own an iPod but want an even smaller version," said Susan Kevorkian, an industry analyst at consultants IDC.
Apple's shares more than tripled last year, as the iPod and market-leading iTunes online music store helped boost the brand.
In December, the company issued a lawsuit to prevent online leaks of information about future products.
Apple is due to announce its financial results for the last quarter of 2004 on Wednesday.