To provide a drill screw for mortar by which an outermost woody layer can certainly attached fixedly by one driving work to a compound layer comprising, a first, a woody member, next, a mortar member, and the last, the woody member again.

A tip part 12 is formed into a sharpened pyramid so as to be easily driven into the surface of a woody member, a rod part 14 is formed coaxially from the base part 17 of the pyramid part through a short diametral taper part 13, a screw stripe is so formed on the screw rod part 14 that an outside diameter d1 is set within 90-110% to a maximum diameter D that the end of the ridge line of the pyramid part 12 describes, and an axial total length from the tip to an end is so arranged that the screw part can reach a woody layer when driven into from the surface of a concrete layer having the woody layer at least on its rear surface.