PURPOSE: To provide a structure without bringing an armature into contact with a spool valve and to drive a servo valve by the armature.

CONSTITUTION: A movable armature 20 to be moved in an axial direction to a fixed member 12 is provided on the position of the axial direction from the fixed member 12. A coil 26 is provided around the fixed member 12 and a magnetic flux is generated by a current flowing through the coil 26. The generated magnetic flux generates traction force for moving the armature 20 to the fixed member 12. A housing 42 is provided around the coil 26, the fixed member 12 and the armature 20 so as to house the armature 20, the coil 26 and the fixed member 12. The housing 42 is provided with at least one opening part 44 and fluid is made to flow in and out of the housing 42 and brought into contact with the armature 20. A bleeding device discharges a part of the fluid based on the current to the coil 26 and controls the pressure of output to a predetermined level.