On a bottom surface of a light guide element of an operation device including a panel with a light-transmissive portion, a reflection portion is formed in a first region thereof, which is close to a light source, and a first diffusion surface is formed in a second region of the bottom surface of the light guide element, which is a region distant from the light source. A light-incident side of the light guide element is a non-diffusion surface. Sides other than the light-incident side are second diffusion surfaces. Light that has been emitted from the light source and incident to the light guide element via the light-incident side is totally reflected and is then guided to the first and the second diffusion surfaces and a part of diffusion-reflected light illuminates the light-transmissive portion of the panel.