An actuator according to the present invention includes a telescopic body, a tank, a first opening/closing valve provided in a first passage that connects a rod side chamber to a piston side chamber, a second opening/closing valve provided in a second passage that connects the piston side chamber to the tank, a pump that supplies a fluid to the rod side chamber, a motor that, drives the pump, an exhaust passage that connects the rod side chamber to the tank, and a valve element provided in the exhaust passage, wherein a telescopic unit is formed by integrating the telescopic body, the first opening/closing valve, and the second opening/closing valve, a driving unit is formed by integrating the pump and the motor, and the telescopic unit and the driving unit are provided as separate bodies.