A fastener comprising a head , a shank extending axially from said head and providing a drilling portion opposite to said head , and a threaded portion spirally disposed on said shank , said head having a top face and a conical bottom face extending from said top face to said shank ; wherein said head includes a plurality of cutting portions formed on said bottom face , a plurality of cutting ribs protruding from said bottom face , and a plurality of accommodation rooms formed between said plurality of cutting portions and said cutting ribs , each of said plurality of cutting portions extending from said top face towards said shank , characterized in that each of said plurality of cutting portions including a projecting blade formed circumferentially of said top face at an outer edge thereof and extending in the direction of said shank , wherein said projecting blade decreases progressively in the direction of said shank , each of said plurality of cutting portions further including an adjoining wall and a flank wall respectively connected to said projecting blade and a cutting edge formed at a junction of said adjoining wall and said flank wall , a bottom edge on said flank wall being defined opposite to said cutting edge , each of said adjoining walls extending from said cutting edge of one cutting portion to said bottom edge of said flank wall of another adjacent cutting portion so that each of said adjoining walls extends circumferentially along each of said projecting blades to thereby extend each of said plurality of accommodation rooms from each of said adjoining walls to said shank , said plurality of cutting ribs projecting from said bottom face and extending radially between said cutting portions and said shank to be directed at corresponding ones of said plurality of cutting portions , each of said cutting ribs having two rib walls protruding from said bottom face and meeting at a rib edge . wherein said head includes a plurality of cutting portions formed on said bottom face , a plurality of cutting ribs protruding from said bottom face , and a plurality of accommodation rooms formed between said plurality of cutting portions and said cutting ribs , each of said plurality of cutting portions extending from said top face towards said shank , characterized in that each of said plurality of cutting portions including a projecting blade formed circumferentially of said top face at an outer edge thereof and extending in the direction of said shank , wherein said projecting blade decreases progressively in the direction of said shank , each of said plurality of cutting portions further including an adjoining wall and a flank wall respectively connected to said projecting blade and a cutting edge formed at a junction of said adjoining wall and said flank wall , a bottom edge on said flank wall being defined opposite to said cutting edge , each of said adjoining walls extending from said cutting edge of one cutting portion to said bottom edge of said flank wall of another adjacent cutting portion so that each of said adjoining walls extends circumferentially along each of said projecting blades to thereby extend each of said plurality of accommodation rooms from each of said adjoining walls to said shank , said plurality of cutting ribs projecting from said bottom face and extending radially between said cutting portions and said shank to be directed at corresponding ones of said plurality of cutting portions , each of said cutting ribs having two rib walls protruding from said bottom face and meeting at a rib edge . <EOS>