Prime Minister Shinzo Abe's ruling coalition has won a landslide victory in an election for parliament's upper house, despite doubts about his economic policies and his goal of revising the pacifist constitution.
Abe's coalition and like-minded parties also got the two-thirds "super majority" needed to try to revise the post-war constitution for the first time, some TV exit polls showed, although others said just that it was within their grasp.
Abe's Liberal Democratic Party (LDP) also won a simple majority for the first time since 1989, a win that will bolster his grip over the conservative party.
A push to ease the charter's constraints on the military operating overseas could lead to tension with China, where memories of Japan's past militarism still arouse anger.
In Japan, financial market players fear amending the charter will divert Abe's energy from reviving the stuttering economy.
"Markets want confirmation of Abe's strong grip on power, but they also want Abe to use that power for the economy first, not constitutional reform," said Jesper Koll, chief executive at fund manager WisdomTree Japan.
Some voters who cast a ballot for Abe's LDP said they wanted the same.
"Especially since I see economic growth as the priority, I have little hope for the opposition parties," said Yoshihiko Takeda, a 36-year-old employee of an IT company.
Abe had cast the election as a referendum on his "Abenomics" recipe of hyper-easy monetary policy, spending and reform.
With signs the strategy is failing, the government plans to compile a post-election stimulus package that could exceed 10 trillion yen ($A132.33 billion).
But economists worry the government will choose big-ticket infrastructure projects rather than implement tough structural reforms.
