Tens of thousands of people stood for a minute of silence at 8:15 am at a ceremony in Hiroshima's peace park near the epicentre of the 1945 attack, marking the moment of the blast. Then dozens of doves were released as a symbol of peace.
The US bomb, "Little Boy," the first nuclear weapon used in war, killed 140,000 people. A second bomb, "Fat Man," dropped over Nagasaki three days later, killed another 70,000, prompting Japan's surrender in World War II.
Matsui called nuclear weapons "the absolute evil and ultimate inhumanity" that must be abolished, and criticised nuclear powers for keeping them as threats to achieve their national interests.
He renewed an invitation to world leaders to visit Hiroshima and Nagasaki to see the scars themselves, during the G-7 summit in Japan next year.
Japanese Prime Minister Shinzo Abe, also addressing the ceremony, said that as the sole country to face a nuclear attack, Japan had a duty to push for the elimination of nuclear weapons.
He pledged to promote the cause through international conferences to be held in Hiroshima later this month.
