To prevent generation of cam out by making an angle formed by a line of a valley stripe extending in an axial direction between each blade part forming a tip part of a screwdriver into a cross shape and an axis of a driver bit almost 0 degree.

A screw driver 10 is provided with four blade parts 12 forming a cross at a tip part (bit) 11. In each blade part 12, an inclined surface 12A is formed and thickness is constant in the axial direction. Between each blade part 12, a line 13 of a valley stripe extending in the axial direction of the bit 11 and an axis 14 of the bit 11 are made parallel, and an angle formed by the line 13 of the valley stripe for the axis 14 is made almost 0 degree. As a result, the inclination of an axis misalignment becomes small and generation of cam out can be prevented.