PURPOSE: To prevent any unexpected action of a piston during releasing action of a brake mechanism and also to simplify control action.

CONSTITUTION: A four-position switch valve 6 is connected to operation chambers 1a and 1b of a cylinder body 1. A position switching action control circuit 35 and an action commanding circuit 36 are connected to both pilot valves 27 and 27 of this switch valve 6. In addition, the control circuit 35 is provided with a brake canceling action control circuit 37 for actuating an electromagnetic valve 33 for controlling the release of the brake 31 of a cylinder. In the case where both operation chambers 1a and 1b are in a non-pressurized state, pressurized fluid is temporarily supplied to both operation chambers 1a and 1b by the position switching action control circuit 35, and then a brake releasing action signal is output.