Yoshimi Watanabe, the head of the minor opposition Your Party, on Friday insisted an undeclared 800 million yen loan had been spent on personal items, including a lucky bamboo rake.
Watanabe has admitted receiving the funds from the chairman of leading cosmetic company DHC Corp, but denies it had anything to do with his political work.
"I borrowed the money purely personally," Watanabe told reporters. "I decided how to use it, and obviously I do not believe it was illegal."
Japanese law requires that all political donations be made public.
Watanabe said he no longer has the money after spending it on "miscellaneous items" including a decorative "kumade" -- a bamboo rake believed to confer luck on its holder.
The claim drew sneers from media and political colleagues.
"I never knew there was such an expensive 'kumade' in this world," said Akira Amari, state minister in charge of economic and fiscal policy.
"Mr Watanabe always says politicians need to be accountable. I am sure he will offer a persuasive explanation."
But Watanabe's luck appeared Friday to be running a little low, with his benefactor, Yoshiaki Yoshida, chairman of DHC, telling Jiji Press he was not being truthful.
"What he has said was untrue," Yoshida told the agency. "I still have a mobile phone message from him saying he needed money for his electoral campaign."© (c) 2014 AFP