Prosecutors are expected to launch an investigation into former Tokyo Gov. Naoki Inose, who stepped down at the end of last year over his receipt of ¥50 million from one of the country's largest hospital chains, the Tokushukai Group, sources said Tuesday.

The Tokyo District Public Prosecutor's Office plans to question Inose, 67, after it accepted a complaint filed by members of a civic group who claim the money was not listed in Inose's funds report for his Tokyo gubernatorial election campaign in violation of the Public Offices Election Law.

They also argue the money may have been provided in exchange for Inose's favorable treatment for Tokushukai, which aimed to acquire a hospital operated by beleaguered Tokyo Electric Power Co.

As governor, Inose had the power to approve the opening of hospitals.

Inose received the money from House of Representatives member Takeshi Tokuda, son of Tokushukai founder Torao Tokuda, in November 2012, and won the gubernatorial election the following month.

Inose said he borrowed the ¥50 million in a personal capacity and therefore the money was not reported as election campaign funds to authorities.

Tokushukai is at the center of another election violation case involving Takeshi Tokuda, in which some of his family members, including his mother, have been indicted for buying votes in the 2012 general election.

Inose is believed to have received the loan from Takeshi Tokuda. A story in November quoted a source at Tokushukai-run hospital in Kamakura, Kanagawa Prefecture, where Torao Tokuda is being treated, as saying Inose initially sought ¥100 million for his campaign war chest.