Only a handful of reactors have come back online, due to public opposition, since the Fukushima disaster in 2011. Tuesday's move comes after court clearance.
In a small victory for the government's pro-atomic push, a Japanese utility switched on another nuclear reactor on Tuesday, despite strong public opposition after the 2011 Fukushima meltdown.
The restart of the No 3 reactor at the Takahama nuclear plant brings the number of operational atomic reactors in Japan to five, while dozens more remain offline. Located in Fukui prefecture, the plant which is operated by Kansai Electric Power (KEPCO) is some 350 kilometres (215 miles) west of Tokyo.
Tuesday's move comes after the utility switched on Takahama's No 4 reactor last month with the court's go-ahead, in spite of complaints from local residents over safety concerns. The court also gave the green light to switch on the No 3 reactor.
Japan shut down all of its atomic reactors after a powerful earthquake in March 2011 spawned a huge tsunami that led to meltdowns at the Fukushima nuclear plant.
Fukushima became the worst nuclear accident since Chernobyl in 1986.
Since then, just a handful of reactors have come back online due to public opposition and as legal cases work their way through the courts.
However, Prime Minister Shinzo Abe has aggressively promoted nuclear energy, calling it essential to powering the world's third-largest economy.
Much of the public remains wary of nuclear power after the disaster at Fukushima spewed radiation over a large area and forced tens of thousands to leave their homes, with some unlikely to ever return.