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 an inner side surface of the optical member and that reflects the illumination light outward in the radial direction. The optical member includes a light guide layer that receives the illumination light from the output end and that guides the illumination light and a diffusion layer that is located outside the light guide layer in the radial direction and at one end of the light guide layer in a direction along the axis and that receives the illumination light from the light guide layer and guides the illumination light while diffusing the illumination light.
