A backlight (illumination device) of this invention includes a plurality of light source units (12) each including (i) at least one light source (5) and (ii) a light guide body (7) for surface-emitting light which has come from the at least one light source. In the light source unit (12), the light source is disposed at one end portion of the light guide body (7), and another end portion of the light guide body (7), opposite to the one end portion, has a thickness from 0.05 mm to 0.15 mm. As a result, it is possible to further improve luminance uniformity in an illumination device including a plurality of light guide bodies.