Yoshiaki Murakami said he was surprised when prosecutors accused him of trading on advance knowledge of a high-profile takeover bid but admitted his actions could be interpreted as breaking securities laws.
"Rather than spend two years fighting about it in court, I decided the best thing would be to agree with the prosecutors," he said on Monday.
"I consider myself a pro among pros in this securities market. I had to consider the outside possibility that I had made a mistake," he added.
The former Japanese trade ministry official insisted he was proud of his financial achievements and attacked corporate Japan and its media, saying they were hostile to those who challenged the system.
Despite his defiant tone, he said he would resign immediately from the $3.6 billion Murakami investment fund which he runs and would not return to the world of securities trading.
Possible jail time
Murakami faces up to three years in prison or a fine of up to ¥3 million ($26,890).
According to local media, Tokyo prosecutors and the Securities and Exchange Surveillance Commission suspect that the fund bought a large quantity of shares in Nippon Broadcasting System last year, based on advanced knowledge that internet firm Livedoor would make a takeover bid for the company
In February 2005, Livedoor said it acquired a 35% stake in Nippon Broadcasting and the Murakami Fund is reported to have sold part of its stake to Livedoor.
Livedoor ultimately withdrew its bid for NBS after a bitter fight and settled for a compromise deal that gave control to Fuji Television Network, an NBS affiliate that was fighting Livedoor for control of the radio firm.