A disk brake capable of stabilizing welding quality of friction stir welding. In the disk brake, a brake pad (33) is pressed against a disk (2) by a piston (6) caused to slide in a bore (38) of a cylinder (45). The cylinder (45) is constituted by a cover member of a bottom portion and a cylinder main body (58) having an opening closed by the cover member (53) welded by friction stir welding. A thickness of an inner side of the cylinder main body (58) in a disk radial direction is greater than a thickness of an outer side of the cylinder main body (58) in the disk radial direction.
