Operation device and image reading apparatus

An operation device comprising:

• a panel including a light-transmissive portion having a specific shape;
• a light guide element having a first surface, a second surface, and a plurality of sides, the first surface facing the panel;
• a light source located opposite a predetermined light-incident side of the light guide element;
• and
• an electrode provided at a location corresponding to the light-transmissive portion closer to the second surface of the light guide element and configured to detect a capacitance,
• wherein a reflection portion is formed in a first region, which is close to the light source, of the second surface of the light guide element, a first diffusion surface, corresponding to a range including the light-transmissive portion, is formed in a second region more distant from the light source than the reflection portion, and the light-incident side of the light guide element is a non-diffusion surface and the sides other than the light-incident side are second diffusion surfaces, and
• wherein light that has been emitted from the light source and incident to the light guide element via the light-incident side is totally reflected on the reflection portion and on the first surface and is then guided to the first and the second diffusion surfaces and a part of diffusion-reflected light illuminates the light-transmissive portion.