To provide a wrench offering simple construction permitting a reduce in cost and allowing the tightening or loosening of various bolts and nuts different in size without changing parts.

A wrench comprises a fixed portion 3 provided at the end of a gripping portion 2, a movable portion 4 constituting an annular body 16 together with the fixed portion 3, when pivotally mounted on the fixed portion 3 and closed, locking means 5 for locking a free end 18 of the movable portion 4 to the fixed portion 3, and an engaging member 6 for inwardly energizing the fixed portion 3 and/or the movable portion 4.