Shoichi Nakagawa, chairman of the Liberal Democratic Party (LDP)'s Policy Research Council, said Japan will adhere to its policy of not arming itself with nuclear weapons, but added that a debate on the issue was necessary.
"We need to find a way to prevent Japan from coming under attack," Nakagawa told a television programme, referring to what Tokyo should do following the reported North Korean nuclear test.
"There is argument that nuclear weapons are one such option. I want to make clear that I am not the one saying this, and Japan will stick to its non-nuclear principles, but we need to have active discussions," he said.
Nakagawa said the constitution does not prohibit the possession of nuclear arms, adding that having such weapons could reduce or remove the risk of being attacked.
While some analysts have pointed out the possibility of Japan -- the only nation to suffer an atomic bombing -- seeking nuclear weapons in response to North Korea's announced nuclear test, Japanese Prime Minister Shinzo Abe has flatly rejected the idea.
Japan has stuck to self-imposed "three principles" that ban the possession, production and import of nuclear arms, and politicians who even questioned the ban in the past were met with fierce criticism.
A former parliamentary vice defence minister resigned in 1999 after suggesting in a magazine interview that parliament should debate nuclear arms.
But faced with the threat of North Korea's nuclear and missile programmes, the nuclear taboo is easing among the public and more lawmakers now challenge the ban without receiving the disapproval they would have in the past.
The UN Security Council voted unanimously on Saturday to impose financial and weapons sanctions on North Korea in response to its announcement on Monday that it had successfully conducted a nuclear test.

Copyright Reuters, 2006