Exit polls showed the Liberal Democrats (LDP) winning nearly 300 seats in parliament's 480-member lower house. Its ally, the New Komeito party, looked set to win 30 seats.
That would give the two parties the two-thirds majority needed to overrule parliament's upper house and break a deadlock that has plagued the world's third biggest economy since 2007.
An LDP win will usher in a government committed to a tough stance in a territorial row with China, a pro-nuclear energy policy despite last year's Fukushima disaster, and a potentially risky prescription for hyper-easy monetary policy and big fiscal spending to beat deflation and tame a strong yen.
The LDP is expected to be friendly to nuclear utilities, although deep public safety concerns remain a barrier to business-as-usual for the industry.
China's official Xinhua news agency said in an editorial it was a "troubling sign" that some parties in the election had promised to take a tough stand on territorial disputes and increase military spending.
The agency said Japan should formulate its foreign policy with a long-term perspective to repair ties with neighbours.