Bolt or nut tightening device having reaction force receiving member

A bolt or nut tightening device having a tightening socket engageable with the bolt or nut to be tightened and operatively associated with a motor through a speed reduction mechanism, said tightening device comprising:

• a reaction force receiving member adapted to be brought into contact with a projection positioned in the vicinity of the bolt or nut to be tightened and for receiving a reaction force of tightening when brought into contact with the projection during tightening operation,
• detecting means for detecting the completion of tightening of the bolt or nut;
• a controller coupled to the motor, and operable to deenergize the motor in response to a tightening completion signal from the detecting means and to reversely rotate the motor only for a moment upon lapse of a predetermined period of time taken for inertial rotation of the motor to reduce to an extent neglectable for the reverse rotation of the motor after the deenergization;
• and
• said reaction force of tightening, which has been received by the reaction force receiving member, being released by the reverse rotation of the motor only for a moment after the deenergization thereof when the controller receives the tightening completion signal from the detecting means.