PURPOSE: To reduce a jig tool cost and the number of working processes and to provide bits having difference lengths by using a single driver by a method wherein the bit part of the driver is provided with an expansion and contraction function.

CONSTITUTION: A bit part is gradually narrowed in the direction of a tip making contact with a screw, spring type stoppers 2 are provided in the direction of the root of each of parts (a) and (b), and holes 1 for stopping a stopper are formed in the direction of the tips of parts (b) and (c). When the length of a bit pert is increased to a maximum, the parts (a) and (b) are extended from the part (c), and when the part is extended to a maximum, the stopper 2 is protruded from the hole 1 for stopping a stopper. This method prevents expansion and contraction of the bit part and secures the bit part. When the parts (a) and (b) are intended to be contained in the part (c), the stopper 2 of each of the parts (a) and (b) is pressed down through the hole for stopping a stopper of each of the parts (b) and (c). With this state, the parts (a) and (b) can be pushed and contained in the part (c).