Six people linked to Liberal Democratic Party lawmaker Takeshi Tokuda were arrested Tuesday on suspicion of illegally rewarding people who worked on the Lower House member's campaign for the December 2012 general election, Tokyo prosecutors and police said.

The suspects are two older sisters of Tokuda and four executive members of the Tokushukai hospital and welfare chain founded by Tokuda's father, Torao, according to the prosecutors and police.

While the 75-year-old Torao, a former Lower House lawmaker, is listed as one of the suspects in the case, he was not arrested as he is suffering from a motor neuron disease.

Tokuda, 42, told LDP Secretary-General Shigeru Ishiba on Tuesday evening he will leave the LDP.

"I can't cause more trouble to the party," Tokuda told reporters after meeting with Ishiba in Tokyo.

Ishiba is expected to accept Tokuda's departure.

According to the prosecutors and police, the suspects are two older sisters of Tokuda and corporate executives — 50-year-old Narumi Koshizawa and 46-year-old Michiyo Stern — as well as four executive members of the Tokushukai hospital and medical facilities chain founded by Tokuda's father — Ichiro Ishikawa, 58, Giichiro Oketani, 69, Masahiko Okuda, 69, and Hirotaka Kitaguchi, 53.

The prosecutors said 563 campaigners are believed to have received a total of ¥147.5 million, the largest-ever corruption case of its kind. Tokuda may lose his Diet seat if his relatives are convicted.

The six suspects allegedly provided the campaigners with rewards and air tickets between November 2012 and July.

Elected to the Lower House in 2005, Tokuda, from the Kagoshima No. 2 district, was appointed last December as parliamentary secretary in charge of infrastructure and transport as well as reconstruction from the March 2011 disasters. He quit that post in February after a scandal broke over a relationship with a woman.