A screw includes a positioning member defined on inclined cutting planes of a drilling portion of the screw for stably allowing a cutting edge constructed at a convergence of the cutting planes to cut efficiently. A threaded section formed on a shank of the screw is extended toward the cutting edge and connected with one end of the cutting edge. The positioning member helps the screw fixedly stand on an object. The cutting edge and the cutting planes allow cutting debris to be swiftly and smoothly extruded therefrom into the threaded section for avoiding the piling of the considerable cutting debris. Thereby, the screwing torque is reduced and the drilling speed is promoted. Preferably, the fastened screw is sunken in the object, and the fastening operation is completed successfully.