Abstract: In order to prevent breakage in a resin near the peripheral edge part of a metal reinforcement plate of a plate insert type ramp due to heat shrinkage without increasing wall thickness of the resin near the peripheral edge part of the plate or without reducing the thickness of the plate, a part or all of the peripheral edge parts of the reinforcement plate are exposed from the front surface of the ramp body, the reinforcement plate being exposed from the front surface of clearance portions between a plurality of disk insertion parts formed at one of four sides of the ramp body and/or the peripheral edge parts of the ramp body at its other three sides.