The camera and medical equipment maker said on Tuesday that 48 institutional investors and pension funds, mostly foreign investors and pension funds including the Teachers' Retirement System of the State of Illinois and Pioneer Asset Management SA in Luxembourg, had filed the suit in Tokyo District Court.

"It is still unclear at this point how much this may affect our financial results," said Olympus spokesman Tsuyoshi Oshima.

Speaking at a quarterly earnings briefing on Monday, Olympus President Hiroyuki Sasa said the firm had accounted for potential lawsuits from shareholders in its outlook for the financial year to March.

The firm lifted its annual net profit forecast to 8 billion yen from 7 billion yen, sparking a 5.9 percent rise in its share price on Tuesday.

The news of the shareholder lawsuit came after the close of Tuesday's share trading.

Shares in Olympus sank nearly 60 percent in 2011 due to the $1.7 billion accounting fraud, which came to light in October of that year. The shares have recaptured some of that lost ground this year, gaining 30 percent compared with a 2 percent rise in Tokyo's benchmark Nikkei average .N225.

Three former Olympus executives and the company itself pleaded guilty in a Tokyo court in September to charges related to the scandal, which forced it to restate several years of earnings.

($1 = 79.4200 Japanese yen)

(Reporting by Mari Saito; Editing by Michael Watson)

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