In March 1990, as mayoral elections was underway,
Manzo Hamamoto, a member of the Upper House of the
Diet from the Japanese Socialist Party, suggested to Hiraoka to run for mayor. He declined at first, also for lack of funding, but was persuaded to run as
Osamu Hashiguchi, Chairman of the
Hiroshima Chamber of Commerce and Industry, promised the required funding. He was elected mayor of Hiroshima in February 1991. Soon after becoming a mayor, Hiraoka had to deal with his first crisis, when on March 14, 1991, a bridge collapsed in
Asaminami-ku, killing 15 people. Relatives of the dead filed a lawsuit against the Hiroshima municipality for compensations, but Mayor Hiraoka contended the city was not to blame. The lawsuit was eventually dropped in 1998. As mayor, Hiraoka worked to further cooperation between Hiroshima and cities in
South Korea, thus leading to the Hiroshima-
Daegu sister city agreement in 1997. The 1994
Asian Games were held in Hiroshima and hosted by Hiraoka as Mayor. His anti-nuclear activities led him to appear in 1995 as representative of the Japanese government in the International Court of Justice hearing on the legality of nuclear weapons. In late 1998, Hiraoka announced he will not run for third term as mayor, citing low voter participation in the 1995 mayoral election as an obstacle to any mayor wishing to have the people's approval. He did not run in the 1999 mayoral election, and retired after eight years of serving as Mayor of Hiroshima. ==Post mayoral activities==