Disclosed herein is a tapping screw (1) exerting an excellent anti-loosening effect with regard to a workpiece made of a soft material such as resin and an aluminum alloy. The tapping screw (1) includes a shaft part (3), and a normal thread (10) which is formed on the outer circumferential surface of the shaft part. A clearance groove (20) is formed by cutting out a portion of a ridge of the normal thread, and an engaging protrusion (30) is provided on a bottom of the clearance groove along a portion or an entirety of an edge of the bottom that continuously extends from a flank surface of the normal thread. The tapping screw (1) exerts an excellent anti-loosening effect even when a workpiece expands, contracts or oscillates because the engaging protrusions (30) are embedded into portions of the workpiece which have been embedded into the clearance grooves (20).