PURPOSE: To contrive simplification or the like of a cam structure by providing a communication path between fluid chambers on both sides of the axial direction, partitioned by a piston, and protrusively providing a cam passive section in either a cylinder internal peripheral surface or a piston peripheral surface while forming a cam groove in the other.

CONSTITUTION: A brake 1 comprises a cylinder 3 closed with both ends by an end cover 2, piston 4, shaft 7 and a cylinder cover 8. When the cylinder cover 8 is rotated by fixing a fixed part 28 of the shaft 7, turning force, in which a roller 13 of a cam passive section 14 tends to rotate a side surface of a cam groove 24 of the piston 4 in the peripheral direction, is generated, and the cylinder 3 is slowly rotated while receiving braking force by reciprocation-moving the piston 4 in the axial direction on a spline tooth 27 with axial directional force, in accordance with a tilt angle of the groove 24, acting on it. On the other hand, operating fluid in fluid chambers 3A, 38 passes through a communication path 32 to flow in a reverse direction to the sliding direction of the piston 4 by its axial directional movement, and a flow of this operating fluid generates resistance of the axial directional movement of the piston 4 to give braking force to the cylinder 3.