A sound generating mechanism 60 includes a sounding member 61, a retaining member 62, a sounding pin 64, and a coil spring 65. The sounding member 61 includes a disk portion 61a formed into a ring shape, a plurality of sounding concavities 61b formed circumferentially apart on the disk portion 61a, and engagement portions 61c integrally formed with the disk portion 61a. The retaining member 62 prevents the sounding member 61 from falling off. The sounding pin 64 is mounted in the knob member 56 at a position opposite at least one of the sounding concavities 61b so as to be movable toward and away from the sounding concavities 61b. The coil spring 65 urges the sounding pin 64 toward the sounding concavities 61b. The sounding pin 64 is unlikely to fall off when the knob member 56 is attached to or removed from the knob mounting portion 52.