"We welcome it as a forward-looking move... but an important thing is whether the move will lead to the complete abandonment of missile and nuclear developments in a verifiable and irreversible manner," Abe told reporters.
"We want to watch it closely."
North Korean leader Kim Jong Un pledged Saturday his country would halt nuclear tests and intercontinental missile launches, a move welcomed by US President Donald Trump and South Korea.
But Defence Minister Itsunori Onodera said earlier that Japan "can't be satisfied", because Pyongyang did not mention giving up short- and medium-range ballistic missiles.
Japan's Prime Minister Shinzo Abe. Source: AAP
Onodera said Tokyo would persist with its policy of putting pressure on Pyongyang so that it ultimately gives up its "weapons of mass destruction, nuclear arms and missiles".
Japan, a close US ally in the region, is in the direct firing line of North Korean missiles and saw two fly over its territory in 2017, sparking outrage and raising tensions to fever pitch.
Japan's Deputy Prime Minister and Finance Minister Taro Aso also voiced scepticism.
"(North Korea) has made a lot of promises and we paid money on the condition that they will give up experiment sites, but they continued," Aso told reporters in Washington, referring to Pyongyang's nuclear programme.
The North's declaration, long sought by Washington, comes less than a week before Kim meets South Korean President Moon Jae-in for a summit, ahead of a much-anticipated encounter with Trump himself.
Earlier this week, Abe held talks with Trump in Florida and displayed a united front on North Korea, including on the issue of Japanese abductees taken to North Korea, a major domestic issue.
