To prevent movement and dislocation of a bit tip during use for fastening and unfastening of a screw with a cutting edge being inserted in a groove by a method wherein recess-form offset protection parts are formed in the bit tip of a flat tip screwdriver.

A flat tip (-) screwdriver 1 is used for fastening and unfastening a screw by inserting a bit tip 2 in the screw head groove of a minus (-) screw. Even when a tip is moved in a sliding state, by pressing a screw by recess-form offset protection parts 3, the screw is collided with the protrusion part of the offset protection parts 3 formed at two ends. The bit tip 2 is protected from dislocation of it from the screw head groove and used as it is.