First to third inner locking pieces 12 to 14 are provided at both ends of an inner shim plate 2a in a radial direction of a rotor so as to be bent toward the pad, respectively. First to third outer locking pieces 15, 17 and 18 are provided at both ends of an outer shim plate 1a in the radial direction of the rotor so as to be bent in the same direction as the locking pieces 12 to 14. An inner shim plate 2a is mounted on a pressure plate 10, and the first to third outer locking pieces 15, 17 and 18 are superimposed on the first to third inner locking pieces 12 to 14 such that main body parts 7 and 8 of the respective shim plates 2a and 1a are locked in the pad in the axial direction of the rotor.