A switch device includes: a voltage dividing circuit that outputs a voltage dividing value corresponding to a conduction state of each of a first switch and a second switch to an output line; an operation interface including a dial which rotates in accordance with a user operation; a rotation detection circuit that detects (i) rotation of the dial by a predetermined angle and (ii) a rotation direction of the dial, and generates an angle signal which includes a pulse indicating detection of the rotation by the predetermined angle, and a direction signal which indicates whether the rotation direction is a first direction or a second direction; and a selection circuit that selects whether to output the pulse of the angle signal to control the first switch or to output the pulse to control the second switch, according to whether the direction signal indicates the first or the second direction.