Daio Paper Corp. filed a criminal complaint Monday against former Chairman Mototaka Ikawa on suspicion of an aggravated breach of trust, while prosecutors will probe his massive borrowings from group firms within a couple of days, investigative and other sources said.

The special investigative squad of the Tokyo District Public Prosecutor's Office has already questioned the 47-year-old grandson of the papermaker's founder, Isekichi Ikawa, on multiple occasions on a voluntary basis, the sources said.

Ikawa has not denied allegations that he repeatedly borrowed money from companies in the Daio Paper group, they said.

The sources said that the prosecutors suspect Ikawa spent almost all of the borrowings on gambling at casinos, in light of bank records of deposits and withdrawals and information from related sources.

Daio Paper's in-house investigative committee earlier said it found Ikawa instructed the firm's seven consolidated subsidiaries to remit a total of ¥10.68 billion to various bank accounts, including his own, between May 2010 and last September. The bank accounts also included those of companies related to casinos.

He had repaid ¥4.75 billion of the loans by the end of October, with the remaining ¥5.93 billion still unpaid. He stopped short of providing detailed explanations on how he spent the money when questioned by the in-house panel.