The illumination device 10 according to the present invention includes: a housing member 22 having a bottom plate 22a and a side wall 22b; a light guide plate 26 disposed on the inside of the side wall 22b in a manner so that a gap is formed between the side wall 22b and the side edge face 26b of the light guide plate 26; a light source unit having a light source 24 and a light source substrate 25 and disposed in the gap in a manner so that the substrate surface 25a faces the side edge face 26b; an optical sheet 23 disposed on the front surface 26a side of the light guide plate 26 and having an outer edge 23d protruding towards the light source substrate 25 from the side edge face 26b in a manner so as to cover and hide the bottom plate 22a at the section where the gap is; and a circulation hole X that pierces the light source substrate 25 or the housing member 22 in a manner such that the outside communicates with the air space S1 enclosed by the side edge face 26b, the substrate surface 25a, the bottom plate 22a, and the outer edge 23d.