A radially mounted disk brake has a caliper body secured to a support member secured to a vehicle body. The caliper body has mounting holes extending in a direction perpendicular to the axis of rotation of a disk rotor. Large-diameter hole portions are formed at the openings of the mounting holes on the side thereof closer to the support member. The large-diameter hole portions are fitted with the side wall surfaces of cylindrical step portions provided on the support member in such a manner that gaps are formed between the bottoms of the large-diameter hole portions and the distal end surfaces of the step portions. The center of the axial length of each mounting hole is positioned radially outward of the disk rotor in the axial direction of the mounting hole with respect to a shortest-distance portion of the caliper body at which the distance between the center of a cylinder bore and the mounting hole is shortest.