Marking the 66th anniversary of the world's first atomic bombing at an annual event usually devoted to opposing nuclear weapons, Kan said the ongoing Fukushima crisis meant Japan must turn to other energy sources.
"The large-scale, long-running nuclear accident has triggered radiation leakage, causing serious concerns not only in Japan but also in the world," Kan said at a memorial ceremony in Hiroshima's Peace Park.
"I will reduce Japan's reliance on nuclear power, aiming at creating a society that will not rely on atomic power generation," he added.
A city official said around 50,000 people took part in the ceremony to remember the 1945 atomic bombing, which killed an estimated 140,000 people instantly or due to burns and radiation sickness soon after the blast.
Over 70,000 perished as a result of another US atomic attack on the port of
Nagasaki three days later.
Saturday's ceremony was attended by representatives of more than 60 countries including the United States.
Kan has pledged to boost alternative energy sources to 20 per cent of the nation's energy mix by the 2020s.
But the embattled prime minister has been fighting calls to resign amid rock-bottom poll ratings, while his government is still struggling to control the crippled Fukushima nuclear plant.