To provide an impact wrench which can easily carry out the adjustment and setting of the operational parameters in a shut-off mechanism, and is excellent in the workability and operability, and further can effectively transmit the torque caused by oil pulses to an anvil by supporting a portion to be struck at the time of striking the portion to be struck by means of an impact portion in the rotary impact mechanism.

The air shut-off mechanism for driving the impact wrench comprises a pressure reducing device communicated with working oil in a liner, a driving rod driven by the hydraulic pressure of the oil passing the pressure reducing device, a shut-off valve for shutting off the supply of high pressure air to a pneumatic motor by interlocking with the driving rod, and a pressure setting means for applying a required pushing force to the rear end of the driving rod by arranging an elastic member so as to be adjustable.