A returning device of a wrench tool contains a body including a tool segment disposed on at least one end portion thereof and having two jaws, an engaging face of at least one of the two jaws including a recessed section in which a receiving groove with a stop rim is formed, the stop rim including a slot fixed on an eccentric position thereof; an auxiliary retainer inserted in the receiving groove and having a retaining portion; a positioning shaft including a front end connected at an eccentric position of a rear end of the auxiliary retainer and including a rear end extending out of the slot and allowing to prevent the auxiliary retainer from disengagement from the receiving groove; a resilient element used to push the auxiliary retainer so that the retaining portion extends out of the recessed section of the at least one of the two jaws.