PURPOSE: To reduce the overall length of a device and easily make the device compact without any adverse effect on the feeling of operation.

CONSTITUTION: A cylinder chamber 20 is separated into two pressure chambers 20a and 20b, and a damper mechanism 41 is fitted to the body of a piston 23 having an output rod 3. Furthermore, the damper mechanism 41 has a main piston 42 fitted with an orifice 43 and fixed to the rod 3, and a free piston 51 forming both damper chambers 55 and 56 communicated to each other at both sides of the piston 42 via the orifice 43 and freely slidable for the rod 3. In this case, the air as a fluid is sealed into both chambers 55 and 56.