A disc brake pad assembly (14, 14a), comprising: a pad which includes a lining additionally attached to a front surface of a pressure plate (2, 2a) and which is disposed at a portion facing an axial side surface of a rotor; and a shim plate, wherein the shim plate includes a flat plate-shaped main body portion, and a plurality of locking pieces (20, 21) which are bent from circumferential edge portions of the main body portion towards the pressure plate, the locking pieces (20, 21) are brought into abutment with circumferential edge portions of the pressure plate (2, 2a) so as to be displaced in a rotating direction of the rotor in such a state that the main body portion is fittingly superposed on a back surface of the pressure plate (2, 2a), characterized in that projecting portions (22a, 22b, 22c) are formed at portions of the circumferential edge portions of the pressure plate (2, 2a) which are brought into abutment with one surface of each of the locking pieces (20, 21), a circumferential central portion of a part of each of the projecting portions (22a, 22b, 22c) which faces the one surface projects further than both circumferential end portions thereof, and the circumferential edge portion of the pressure plate (2, 2a) and the one surface of each of the locking pieces (20, 21) are spaced apart from each other at portions of the one surface which lie close to both circumferential end portions thereof, wherein the disc brake pad assembly (14, 14a) has locking recess portions (11, 15, 15a, 15b, 15c) which are formed in the circumferential edge portion of the pressure plate (2, 2a), the locking recess portions (11, 15, 15a, 15b, 15c) are concave further radially inwards than both side portions which lie circumferentially adjacent thereto, a circumferential widthwise dimension of at least one of the locking recess portions (15, 15a, 15b, 15c) is larger than a circumferential widthwise dimension (w) of a respective the locking piece which is provided in the at least one locking recess portion (15, 15a, 15b, 15c), and each of the projecting portions (22a, 22b, 22c) is formed at a portion of the circumferential edge portion of the pressure plate (2, 2a) which corresponds to a bottom portion of the locking recess portion (15, 15a, 15b, 15c). a pad which includes a lining additionally attached to a front surface of a pressure plate (2, 2a) and which is disposed at a portion facing an axial side surface of a rotor; and a shim plate, wherein the shim plate includes a flat plate-shaped main body portion, and a plurality of locking pieces (20, 21) which are bent from circumferential edge portions of the main body portion towards the pressure plate, the locking pieces (20, 21) are brought into abutment with circumferential edge portions of the pressure plate (2, 2a) so as to be displaced in a rotating direction of the rotor in such a state that the main body portion is fittingly superposed on a back surface of the pressure plate (2, 2a), characterized in that projecting portions (22a, 22b, 22c) are formed at portions of the circumferential edge portions of the pressure plate (2, 2a) which are brought into abutment with one surface of each of the locking pieces (20, 21), a circumferential central portion of a part of each of the projecting portions (22a, 22b, 22c) which faces the one surface projects further than both circumferential end portions thereof, and the circumferential edge portion of the pressure plate (2, 2a) and the one surface of each of the locking pieces (20, 21) are spaced apart from each other at portions of the one surface which lie close to both circumferential end portions thereof, wherein the disc brake pad assembly (14, 14a) has locking recess portions (11, 15, 15a, 15b, 15c) which are formed in the circumferential edge portion of the pressure plate (2, 2a), the locking recess portions (11, 15, 15a, 15b, 15c) are concave further radially inwards than both side portions which lie circumferentially adjacent thereto, a circumferential widthwise dimension of at least one of the locking recess portions (15, 15a, 15b, 15c) is larger than a circumferential widthwise dimension (w) of a respective the locking piece which is provided in the at least one locking recess portion (15, 15a, 15b, 15c), and each of the projecting portions (22a, 22b, 22c) is formed at a portion of the circumferential edge portion of the pressure plate (2, 2a) which corresponds to a bottom portion of the locking recess portion (15, 15a, 15b, 15c).