A wrench includes a wrench body having a ring portion and a handle portion. A retainer that holds a plurality of wedge members is disposed inside the ring portion. Wedge guide grooves are formed on the inner circumferential surface of the ring portion. Each of the wedge guide grooves has a free region which maintains the corresponding wedge member in a free state, and left-hand and right-hand wedge regions each of which maintains the corresponding wedge member in a caught state. The wrench is provided with a changeover mechanism for moving the retainer to a position at which the wedge member faces the corresponding free region, a position at which the wedge member faces the corresponding left-hand wedge region, or a position at which the wedge member faces the corresponding right-hand wedge region.