An ocean current electric power generator includes a mechanical brake that restricts a rotation of a rotor shaft of a rotatable wing, and a power transmission mechanism that is disposed between the rotor shaft and an electric power generator. The power transmission mechanism includes a switching section that switches between a power transmission state and a power disconnection state, a load application section that applies a rotation load on the rotor shaft during the power disconnection state, and a speed varying section that varies a revolution speed of the rotor shaft, and transmits the revolution to the electric power generator during the power transmission state.