A screwdriver bit (50) fitted to a screw wherein generally vertical end wall parts of a specified depth are formed in the bit fitting grooves of a screw head part at the end edge parts, a generally flat bottom part is formed directing from the lower edge part of the vertical end wall parts to the center part of a crew neck part, and a conical bottom surface is formed at its center part, comprising flat blade parts (52) forming, at the top end parts, generally vertical end edge parts fitted into the bit fitting grooves of the screw head part along the vertical end wall parts, the top end surfaces of the flat blade parts being formed in a conical protruded part (54) having an inclination angle θ of approx. 1 to 45° relative to the horizontal plane, whereas the screw having stage parts at the end edge parts of the bit fitting grooves of the screw head part, forming inclined groove parts extendedly directing from these stage parts to the center part of the screw neck part, forming a generally conical bottom surface at its bottom part, and forming wall parts recessed inward from a vertical plane at the end edge parts of the bit fitting grooves through a specified depth.