Koizumi Shinjiro, who chaired the campaign of Japan's Liberal Democratic Party, has stepped down to take responsibility for the party's major setback in Sunday's Lower House election.

Koizumi told reporters on Monday that LDP President and Prime Minister Ishiba Shigeru had accepted his resignation as Chairperson of the Election Strategy Committee.

The LDP maintained 191 seats in the election, but lost 56 it had held.

Koizumi said the party's executives must bear the responsibility for the LDP not achieving its election goal, and as the chairperson, he must take all the blame.

Koizumi also said the LDP failing to resolve its political fund scandal before the election, and not succeeding in winning the public's understanding on the issue led to the outcome.

He called the election result a verdict by voters that the LDP must change, and said the party needs to search its soul and make a fresh start. He added that he will play a role in implementing reforms within the party.

Koizumi was one of nine contenders for the LDP leadership election last month. He finished third and could not advance to the runoff, which Ishiba won.

Ishiba appointed Koizumi as chairperson to handle the campaign. Koizumi, taking advantage of his high profile as a son of former Prime Minister Koizumi Junichiro, traveled across Japan to rally support for LDP candidates.