A pad spring located at the entrance side in the rotational direction of a disk is provided with guide plate portions, radially urging portions that urge a pair of friction pads radially outward of the disk, and circumferentially urging portions that urge the friction pads in the rotational direction of the disk. Each radially urging portion has a projection bent radially inward of the disk. Each guide plate portion has a space portion that allows the projection to abut against the radially inner wall surface of the associated pad guide when the radially urging portion is displaced radially inward of the disk so as to approach the guide plate portion. The circumferentially urging portions are wide plate-shaped members bent from the guide plate portions.