PURPOSE: To simplify structure of a system and ease driving control by providing a damping force changeable mechanism in an oil passage which puts an oil chamber in a cylinder in communication with an accumulator.

CONSTITUTION: When a solenoid valve is opened, pressured oil is introduced into an oil pressure chamber S3 and , due to its pressure, a spool 15 is moved downward against spring force of a return spring 16. A flange part 15a is fitted to a step part 14a because of movement of the spool 15 and, as a result, the oil flowing between a piston rod 2 and an accumulator comes to pass through only slits 15b... provided in the flange part 15a and its passage area is narrowed down. Therefore, flow resistance of the oil becomes high and the damping force generated due to this resistance is adjusted high.