To display a proper torque value for each bit and announce whether a set torque value is correct or not to ensure easy and quick torque setting and prevent the torque value from failing to change.

A torque driver for fastening a screw at a proper torque by the idle running of a bit and a driver mainbody when a given torque is applied to the bit includes an optimum torque value setting and storage part 32 for setting and storing two or more optimum torque values corresponding to the type of the bit, a bit identification part 31 for identifying the type of the bit, a torque value comparison part 33 for comparing a torque value set by a torque value variation part 12 with an optimum torque value for the bit identified by the bit identification part 31 out of torque values stored in the optimum torque value setting and storage part 3, a display lamp 35 for announcing the comparison result of the torque value comparison part 33 and an optimum toque value display part 38 for displaying an optimum torque value stored in the optimum torque value setting and storage part 32 when the bit is mounted on the driver mainbody.