A boss for a self-tapping screw includes a main body having an inner peripheral surface and an outer peripheral surface, a plurality of reinforcing ribs connected with an outer peripheral surface, and a plurality of inner wall portions extending parallel to the central axis. Each of the plurality of inner wall portions are disposed at a portion of the inner peripheral surface opposite to a corresponding one of the plurality of reinforcing ribs across the main body. Each of the plurality of inner wall portions includes a specific portion opposite to the corresponding one of the plurality of reinforcing ribs across the main body. The specific portion is closer to the central axis than other portions of the each of the inner wall portions.