To solve problems such as the increment of cost because of being long, large and heavy, the necessity of a special structure and a special tool for preventing dangerous, and the increment of the output of a fluid pressure cylinder as the resistance of a spring device is increased from the starting period of a driving device, or easiness to trouble the spring device.

In a valve driving device 1 which opens/closes a valve by the reciprocating motion of a piston rod 4 directly connected to a piston 3 in a fluid pressure cylinder 2, an auxiliary cylinder 5 for compressing or pressurizing internal fluid by inserting one end 4b of the piston rod 4 is connected to the high pressure side of a pressure intensifier for increasing/decreasing pressure by the ratio of a pressure receiving area so that a low pressure side gas is compressed by a high pressure side fluid pressure, and the compressed gas pressure on the low pressure side of the pressure intensifier is made to serve as a power source when the pressure of the fluid pressure cylinder 2 is eliminated so that the piston rod 4 is operated in a reverse direction by the high pressure side fluid pressure in the auxiliary cylinder 5.