To provide a valve driving device which can be used when there is no supply source of pressurized air or even when there is no pressurized air and there is a danger that flammable gas such as natural gas in a high pressure pipe line is released into the atmosphere and can reduce the weight of an actuator, produce high power, make the whole device compact and inexpensive and fast open and close a valve.

A piston rod 22 is moved forward by sending fluid from a tank 5 pressurized to a predetermined pressure by a pump 6 into a hydraulic cylinder 21. The fluid in the hydraulic cylinder 21 is discharged by opening an opening and closing valve 8 provided in a return pipe 3b between the hydraulic cylinder 21 and the tank 5. The piston rod 22 is moved backward by sending fluid in the high pressure part of a pressure increasing unit 24 into a sub- cylinder 23 by the pressure of fluid in the low pressure part of the pressure increasing unit 24 compressed by the forward movement of the piston rod 22.