Fujitsu shares plunged more than 18 percent on Friday morning after the sprawling information technology firm warned it would likely report a sharp drop in profit this fiscal year.
The Tokyo-listed stock tumbled 18.58 percent to 645.8 yen at the open, as investors reacted to the profit news, which came after markets closed Thursday.
Fujitsu said its annual net profit jumped 24 percent to 140 billion ($1.2 billion) for the just-ended fiscal year, as a weak yen boosted its bottom line.
But for the year to March 2016, the company forecast a much weaker net profit of 100 billion yen on slightly higher sales of 4.85 trillion yen, as it faces a downturn in its home market.
A sales tax rise in Japan last year hammered consumer spending and sent the economy into a brief recession.
Japan reported a small economic expansion in the last quarter of 2014, but consumer spending remains weak.