To provide a screw driver suitable for magnetic recording device using a magnetic head while eliminating the magnetization of a screw by reversing a direction of the current flowing in a coil provided in a driver main body so as to reverse the magnetic pole of a tip of a bit part in a constant cycle.

In a method of fastening a screw with a screw driver, an alternating current power source 4 is applied to a coil 3, and magnetic pole (N/S) are mutually reversed at a tip of a bit part 2. In this continuous reverse condition, a head part 5a of a screw 5 made of the magnetic material is attracted to the tip of the bit part 2, and a screw part 5b of the screw 5 is made to abut on a position for fastening, and thereafter, when the screw 5 is pushed by the bit part 2, a motor is rotated so as to turn the bit part 2, and the screw 5 is fastened. After the fastening, in the condition that the power source 4 is applied to the coil 3, the bit part 2 is separated from the screw 5 so as to conclude the fastening of the screw 5.