A tapping screw provides sufficient tightening force even if used with a thin screwed member and tightening target member. The tapping screw (100) includes a first ridge (11) and a second ridge (12) configured to have incomplete threads that are 180° out of phase. The tapping screw (100) includes a first tightening force improvement ridge (13) and a second tightening force improvement ridge (14) that are set so as to be smaller than the outside diameters of complete thread sections of parallel threaded portions of the first ridge (11) and the second ridge (12) but larger than the inside diameter of the prepared hole are provided in each of areas which are 90° out of phase with the first ridge (11) and the second ridge (12), respectively, such that the tightening force improvement ridges bite into the prepared hole when the screw is fully screwed in.