An illumination device includes a light output unit having an output end an optical member that is disposed in a circumferential direction centered on a predetermined axis and that receives illumination light output from the output end and outputs the illumination light from a surface thereof and a reflective layer that is provided adjacent to a surface of the optical member at an inner side in a radial direction and that reflects the illumination light outward in the radial direction. The optical member includes, in order from one end in a direction along the axis, a light guide layer and a diffusion layer. The light guide layer receives the illumination light from the output end in the direction along the axis and guides the illumination light. The diffusion layer receives the illumination light from the light guide layer and guides the illumination light while diffusing the illumination light.
