A backlight includes a spot-shaped light source and a light guide unit including a light guide arranged to diffuse and surface-emit light from the light source. The light guide unit includes a substrate to dispose and fixate the light source and the light guide. Protruding sections are provided on an incident surface of the light guide upon which light from the light source is incident, so as to protrude in a direction opposite to an incident direction of the light from the light source. Further, the light guide is fixedly disposed on the substrate by connecting the protruding sections to the substrate. As a result, with the illumination device including the light source and the light guide, it is possible to achieve an illumination device with a higher light use efficiency and higher luminance homogeneity.