A worm gear-actuated variable resistance device including a clutch structure, having a worm gear actuated by a worm screw. The worm gear has a toothless sector, and the teeth are engagable by the thread of the screw to rotate the gear to a position in which the screw opposes the toothless sector. The gear is mounted in a housing having a resistive element and a conductive element fixed thereto. The gear has a resilient finger having a stop member thereon which is slidable in a channel in the housing when the gear rotates. The toothless sector and stop member are so arranged relative to the channel in the housing that when the gear rotates in one direction out of contact with the screw, the stop abuts an end surface of the channel which deforms the resilient finger so as to bias the gear in a direction opposite the original turning direction of the gear, thereby to enable the teeth of the gear to reengage with the screw when the screw is rotated in a direction opposite to the direction corresponding to the original rotational direction of the gear to enable rotation of the worm gear to be reversed.