A wrench for tightening a tightening member to another member by revolving the tightening member around its axis, wherein the wrench comprises an inner surface which is attached to the outer surface of the tightening member. On the inner surface, a recess is provided to store a wedge member and is configured by a continuous formation of a slack area and a wedge area. The wedge member is configured to wedge between the outer surface of the tightening member and the wall of the wedge area when the wrench body is rotated in the one direction, in order to place the wedge member in the wedge area, whereby the wrench and the tightening member are unified regarding the relevant direction, enabling the rotation of the tightening member in the relevant direction through the wrench.