A device for constraining a golf club to swing through an arc of predetermined radius comprises an elongated club engaging member formed by a pair of telescoping members. A ring member encircles the golfer's neck and the outer telescoping member extends from the ring member. A bracket on the lower end of the inner telescoping member secures the device to the club shaft. When the player swings the golf club through a stroke the ring member defines the center of the arc of motion of the club, and the radius of the arc of motion is defined by the telescoping members and the ring member. The telescoping members may be spring-biased together, and handles may also extend from the side of the club engaging member so that a player by observing the tilt on the handles will know whether or not he has kept his arms straight during his stroke. A strap may also be worn around the player's neck to act as a guide for the ring member.