A disk brake has a flange portion (52) formed on the outer periphery of a portion of a caliper body main body (46) where an opening (45) is formed. The opening is used for insertion of a cutting tool for machining of a cylinder bore (26). The outer diameter of the flange portion is larger than that of a general surface (51a) of the outer peripheral wall (51) of the bore formed in the caliper body main body. A lid member (43) is secured to the opening by friction stir welding. The flange portion ensures a sufficient welding margin. The overall weight of the disk brake is reduced by minimizing the wall thickness of the general surface of the outer peripheral wall of the bore.
