PURPOSE: To effectively separate a frictional pad during a braking releasing period from a disc rotor so as to prevent the drag of a lining.

CONSTITUTION: A second piston 12 is liquid-tightly and movably inserted on the antidisc rotor side of the cylinder hole 10 of a fixed body 6 through a corner seal 14. The piston receiving part 7a of a movable body 7 is arranged on the antidisc rotor side of the cylinder hole 10. The piston receiving part 7a and the second piston 12 are integrally connected to each other by connecting means such as a connecting bolt 20, welding and a clip and, when braking is canceled, the movable body 7 can be slid in the direction of a pad pushing/pressing part 7b by the restoring force of the corner seal 14 so that the pad pushing/pressing part 7b can be separated from the back surface of the back plate 4b of the other frictional pad 4.