TOKYO (Kyodo) -- A Japanese judge on temporary assignment with the Financial Services Agency is suspected of repeatedly engaging in insider trading by using information obtained through his duties from April to around August, sources familiar with the matter said Saturday.

He is being investigated by the Securities and Exchange Surveillance Commission, the sources said, with the securities watchdog considering to file a criminal complaint with Tokyo prosecutors.

The judge in his 30s, who was in charge of reviewing documents submitted by companies planning tender offers, came under scrutiny in September after the watchdog detected a suspicious transaction, according to the sources.

The FSA said it will respond strictly based on the outcome of the investigation.

Japanese courts assign young judges to administrative agencies to enable them to gain experience in different fields.