Kozo Watanabe said Thursday he has stepped down as the top adviser of the Democratic Party of Japan to take responsibility for a political money scandal.

It was reported Wednesday that one of Watanabe's political organizations had listed his former secretary's home as its office even though it was not used for such purposes for 12 years up to 2004, and reported a combined ¥170 million in ordinary expenditures.

The former aide, Yuhei Sato, is now governor of Fukushima Prefecture.

Watanabe admitted listing his secretary's home as the group's address. He said he did it because under Lower House rules, members can only house their official political fund management bodies, and no other type of organization, in their Diet office building.

It was also reported that the group also forgot to change the name of its leader and accountant even after their deaths.

"I am embarrassed as a politician that I left everything up to my accountants and office staff," Watanabe said. "It is clear that I have management responsibility and I would like to humbly apologize to my supporters and the public."

Watanabe said he will check the organization's spending report, which allegedly had mistakes when sorting out expenses.

"Even looking back on my activities and the expenditure details, I am positive there is nothing shady," Watanabe said. "But I will check all possible documents and if there should be a problem, I will correct it immediately."