Patent ID: 7726412

Claim:
A tightening tool for tightening a fastener, comprising: a motor; a main shaft which engages with the fastener; a clutch disposed between the motor and the main shaft, wherein the clutch rotates the main shaft by transmitting torque from the motor to the main shaft when a load acting on the main shaft is less than a predetermined value, and shuts off torque transmission from the motor to the main shaft when the load acting on the main shaft reaches or exceeds the predetermined value; means for detecting a current flowing to the motor; means for detecting a rotation angle of the main shaft or the motor; and means for determining whether or not a tightening torque of the fastener is normal based upon the rotation angle of the main shaft or the motor detected by the rotation angle detecting means during a period extending from (1) a time at which a current value detected by the current detecting means exceeds a preset value to (2) a time at which torque transmission from the motor to the main shaft is shut off.