PURPOSE: To prevent the partial friction due to the drag of a disk rotor by lockedly engaging both end parts of a pad spring, which elastically repels both friction pads bestriding the disk rotor both in the nonbraking direction and in the outer circumferential direction of the disk rotor, with the side parts of the back plate.

CONSTITUTION: A slide recessed part 2d which is parallel to a disk shaft from the side surface 2c of a friction pad 9 in the support arm 2a of a bracket 2 is provided. A hanging piece 11a of a friction pad back plate 11 is lockedly engaged with this side recessed part 2d. Both end parts of a pad spring 13, which elastically repels both friction pads 9 bestriding a disk rotor 3 both in the nonbraking direction and in the outer circumferential direction of the disk rotor, are lockedly engaged with the side parts of both back plates 11. Thus, the friction pads 9 can be prevented from the partial friction due to the drag of the disk rotor and from the rattle at the time of idle running by both elastic repulsive forces.