To surely prevent a biting phenomenon of a driving hole of a screw and a driver bit.

A slightly projecting projection 14 is formed on the tip of the driver bit 1. Since clearance is formed between the driving hole 20 and an engaging part 10 by allowing this projection to abut on a deep part 21 of the driving hole 20 of the screw 2, when the screw is automatically supplied and this screw is lowered toward a work existing below and is used for an automatic screw fastener for automatically screwing in the screw, even if the driver bit lifts after finishing screwing-in work, the driver bit does not become a state of biting in the driving hole of the screw, the work is not lifted. Thus, generation of a defective product by deforming and damaging the work is wholly eliminated. Since there is no need to shave the engaging part a little from a specified dimension of JIS so that the engaging part does not bite in the driving hole of the screw for conventionally preventing the biting phenomenon, a simple correction of only polishing and adjusting a projecting quantity of the projection is preferable.