A left-side ring magnet and a right-side ring magnet are fastened to a roller-shaped operation part, circumferentially displaced from each other by a certain angle. Magnetic variation generated by rotation of the magnets is detected by a magnetism detection element. Additionally, a left-side stationary magnet and a right-side stationary magnet, with the same magnetic pole, are annexed correspondingly to the left-side ring magnet and the right-side ring magnet, respectively, so that the stationary magnets are arranged with the same proximal arrangement relative to the ring magnets, respectively. With such a structure, two attractive and repulsive forces between the left-side ring magnet and the left-side stationary magnet; and between the right-side ring magnet and the right-side stationary magnet are totally exerted on the operation part, thereby providing a sharp, clear click touch during rotation.