PURPOSE: To control the position with high accuracy by detecting the position of a ram by a position detector and comparing the feedback quantity from the position detector with a position set value by a controller when the ram reciprocates.

CONSTITUTION: The controller 67 is operated and a command is issued from the controller 67 to an amplifier 69 and a current is conducted to a coil 61 of a linear DC motor 59. The force is generated on the coil 61 and a spool 57 of a servo valve 49 is moved to the right direction. A port P and a port B, and a port A and a port T are communicated with each other, respectively and the hydraulic pressure is supplied from a fluid source and the ram 23 is moved to the left side via a piston rod 39. The ram 23 is moved to the left direction and the feedback quantity from the position detector 65 fitted to a part of the piston rod 39 is compared with the preset position set value in the controller 67 and the above-mentioned operation is repeated till the feedback quantity attains the position set value.