A light guide body rotates integrally with an operation knob, has an incident surface that is a concavely curved surface recessed to a side opposite to a light source side, and rotates about a rotation shaft located so as to intersect the incident surface of the light guide body. The incident surface of the light guide body is a concavely curved surface recessed toward the side opposite to the light source (toward a Z1 direction) on a cross-section taken along an X-Z plane.