To provide an adjustable spanner which can meet the diameters of various types of members to be turned, and conduct screwing and unscrewing working the member to be turned easily in a short time.

A body 20 which constitutes an adjustable spanner 10 involves a fixed jaw 24 formed integrally, and at the opposite position to the fixed jaw 24, a movable jaw 30 is formed so as to be slidable. A pressurizing member 60 is fitted so as to rotate integrally with a clamping part 11, and is formed so as to pressurize the insertion piece 32 of the movable jaw 30, supported so as to be incapable of turning against the body 20 when the body 20 is turned clockwise. The pressurizing member 60 is formed so as to be supported rotatably against the body 20 when the body 20 is turned counterclockwise. A member to be turned is clamped between the fixed jaw 24 and the movable jaw 30 so as to be screwed or unscrewed.