To provide a driver bit which can prevent the floating-up of the tip end of the driver bit to be engaged with the engagement groove formed on the head of a screw when the screw is fastened or loosened by the driver bit.

Edges 3 are provided on the abutting surfaces 2 of the driver bit 1 to be brought into contact with the engagement walls 7 in the engagement groove 6 of the screw 4. When the engagement walls 7 are pushed by the abutting surfaces 2, the edges 3 cut into the engagement walls 7 according to a pushing force. The floating-up of the tip end of the driver bit and the breakage of the head portion of the screw by the tip end of the driver bit can be prevented by making the edges 3 cut into the engagement walls according to the fastening force in the case of fastening the screw by the driver bit.