Prosecutors on Friday questioned DPJ lawmaker Joji Yamamoto on suspicion of illegally using 20 million yen of his secretary's salary for personal use, investigative sources said.

Yamamoto, 37, is suspected of taking the money out of 30 million yen in salary paid to the secretary in charge of policy from October 1996 to September 1999, the sources said.

Lawmakers' government-appointed secretaries in charge of policy affairs receive between 7.5 million yen and 12 million yen a year from state coffers based on their age and experience, which is usually paid directly into their bank accounts. Yamamoto, however, reportedly paid the secretary between 50,000 yen and 100,000 yen a month, which he was able to do because he controlled the secretary's bank account.