Shinzo Hamai (浜井 信三, Hamai Shinzō^?, May 28, 1905 - February 26, 1968) was the first popularly elected Mayor of Hiroshima (served 1947-1955 and again 1959-1967). He created Hiroshima's image as a city of peace.

In 1931, he graduated from the Law School of Tokyo Imperial University, and in 1935 became employed by Hiroshima Municipality.

The circumstances of his rise to prominence result from the fact that following the nuclear bombing of Hiroshima, many municipal employees were killed or incapacitated, while Hamai was only slightly injured. At the time of the explosion, he was at his house located about 3.5 km from the epicenter. His house was partly damaged, but he was still able to walk. He immediately began relief work in cooperation with Japanese army authorities.

In October 1945, Shichirō Kihara was appointed the next Mayor of Hiroshima, and in December Hamai became his deputy. Following Kihara's dismissal from his duties in March 1947 by the Allied occupation authorities and the reforms conducted in Japan by General McArthur, first mayoral elections were held in Hiroshima in April 1947. In that election, Hamai ran against five other candidates, which included vice mayor Hisao Yamamoto and city council chairman Tsukasa Nitoguri. He won the election and became the first popularly elected mayor of Hiroshima.