Japan's Securities and Exchange Surveillance Commission has conducted compulsory probes into a judge seconded to the Financial Services Agency on suspicion of insider trading in shares, sources said Saturday.

The judge in his 30s is believed to have traded company shares in his own name and made a profit, based on inside information he acquired during his work at the Corporate Accounting and Disclosure Division of the FSA's Policy and Markets Bureau to examine documents for companies planning to launch tender offers, the sources said.

The Supreme Court assigns young judges to various administrative organizations to broaden their professional experiences.

Since summer, the SESC has been investigating individuals and places related to the judge and scrutinizing his transaction details, aiming to lodge a criminal complaint with the Tokyo District Public Prosecutors Office.

The financial instruments and exchange law prohibits corporate officials privy to important information, such as tender offers, from trading related shares before the information is made public. Government officials with authority over companies are also banned from trading shares based on undisclosed information acquired through their official duties.

In a past insider trading case involving a public servant, a career-track official at the Ministry of Economy, Trade and Industry was indicted without arrest in 2005 for stock trading based on tender offer information related to a subsidiary of a camera maker.

In 2012, a former senior official of the ministry was indicted for trading shares in semiconductor companies based on undisclosed important information.

Both were ruled guilty. Their verdicts have become final.