To provide a driver bit for cross-flat head screw which is capable of effectively preventing a come-out phenomenon of a driver bit, preventing damage when an attaching/detaching operation of a screw is performed in a conventional way, always attaining proper and quick screw attaching/detaching work and improving work efficiency by improving constitution of the tip of an edge part which can be fitted to the bit fitting groove of a cross-flat head screw.

This driver bit is constituted of a driver bit for cross-flat head screw which is applied to a cross-flat head screw provided with a bit fitting groove formed by a pair of a linear grooves constituted of an inclined groove part and a horizontal groove part crossing at the center part of a screw head part. The driver bit is provided with a flat edge part 32 forming an inclined end edge part 33a fitting along the inclined groove part of the cross-flat head screw. The driver bit is provided with a flat edge part 34 forming a horizontal end edge part 35 which is crossed with this flat edge part 32 at a right angle, fits along the horizontal groove part of the cross-flat head screw, extends at a roughly right angle and is abutted on the groove bottom surface of the horizontal groove part. At the tip center part of each edge part 32, 34, a projection 36 fitting in a conical bottom surface provided at the center of the screw head part of the cross-flat head screw.