An impact torque adjusting device of a hydraulic torque wrench enhances the precision of the magnitude of the impact torque generated, shortens the generation period of impact torques, and enhances the durability when rotating in either of two directions, that is, in normal rotation (when tightening) and in reverse rotation (when loosening). A working fluid path 11b communicates with the inside of a liner 7 serving as a high-pressure chamber H and a low-pressure chamber L when an impact torque is formed. A valve body 11d biased in a direction of releasing the working fluid path 11b is disposed in the working fluid chamber 11b. At the rear back side of the valve body 11d, an oil chamber 15e is formed to communicate with a blade insertion part 8a of a main shaft 8 by way of fluid paths 7c, 7d formed in liner lids 7a, 7b. The working fluid path 11b is thereby narrowed depending on an elevation of the pressure of the working fluid in the blade insertion part 8a of the main shaft 8 elevating along with an elevation of the working fluid in the high-pressure chamber H.