A former Japanese state justice minister has left the governing Liberal Democratic Party after prosecutors raided his home and office over suspected vote-buying in a mayoral election in Tokyo's Koto Ward in April.

Kakizawa Mito's notice of departure was accepted by the party on Thursday.

Earlier on Thursday, prosecutors searched Kakizawa's office in the Diet Members' Building in Tokyo's Chiyoda Ward, as well as his home.

This followed last month's search of Kakizawa's office in Koto Ward, as well as the homes of his secretaries and assembly members, over a suspected violation of the Public Offices Election Law.

In Koto Ward's mayoral election held in April, Kakizawa supported candidate Kimura Yayoi who went on to win.

Prosecutors are looking into funds that Kakizawa's office offered to some of Koto Ward's assembly members ahead of the mayoral election.

Kakizawa has said the payments were his mid-campaign contributions for the assembly election -- which was held at the same time as the mayoral election -- and he had no intention of buying votes.

Kakizawa stepped down as state justice minister in late October to take responsibility for proposing the use of paid-online ads in Kimura's mayoral campaign. It was a violation of the Public Offices Election Law.

Kakizawa is a Lower House member elected from a district in Tokyo that covers Koto Ward. The 52-year-old has been elected 5 times and was appointed state justice minister in September.