To attain size reduction in piping, an apparatus and an actuator, and reduce cost by using fluid pressure increased to high pressure by a pump, and also using a simple circuit.

An opening-closing valve 7 arranged in return piping 6 is closed, and a pump 3 is actuated, and when oil of a tank 4 is sent into a cylinder 2 by push-opening a check valve 10, a piston 5 is pushed, and a piston rod moves leftward, and a pin 19 fixed to the piston rod rotates a scotch yoke 20 in the anticlockwise direction, and a driving device being this actuator main body 1 moves forward. A stem 18 of a valve 17 is rotated thereby, and the valve 17 is opened or closed. Next, when the opening-closing valve 7 is opened, a right end part piston 5 of the piston rod 9 pushed by elastic repulsive force of a spring 8 discharges oil in the cylinder 2 to the tank 4 through the return piping 6. The scotch yoke 20 is rotated in the clockwise direction by a rightward movement of the piston rod 9 at this time, and the driving device moves backward.