Former Olympus chairman Tsuyoshi Kikukawa pleaded guilty to charges of falsifying accounts and covering up losses as his trial began on Tuesday.
The camera firm and two other former executives also pleaded guilty, the BBC reported. The three executives could face up to 10 years in prison.
In what has become one of Japan's biggest corporate scandals, the three former executives were charged with taking part in a $1.7 billion accounting cover-up going back years.
Reuters said the scandal came to light last October when chief executive Michael Woodward questioned some dubious deals which had been used to conceal the losses.
"The full responsibility lies with me and I feel deeply sorry for causing trouble to our business partners, shareholders and the wider public," said ex-chairman Kikukawa at the beginning of his trial, according to Reuters. "I take full responsibility for what happened."
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Olympus Executive Vice President Hisashi Mori and Hideo Yamada, a former auditing officer, were the other two who pleaded guilty on Tuesday, to hiding losses that the Japanese camera maker incurred in the 1990s, Bloomberg said.
Olympus admitted that 100 billion yen ($1.3 billion) of securities-related investment losses were secretly moved off its books, starting in the 1990s, according to CNN.
"We’re looking for a strong reaction from the court in terms of a strong sentence," said Jamie Allen, the secretary general of the Asian Corporate Governance Association.
The former executives could face fines up to 10 million yen ($128,000), in addition to their jail sentences, and the company could be fined up to 700 million yen ($9 million), Bloomberg said.
Four financial advisers are also charged with violating securities laws, and will be tried separately from the executives, CNN said.
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