A display device comprising: a display panel; a light source configured to emit light from a rear side relative to the display panel toward the display panel; and a concave reflective sheet disposed on the rear side relative to the display panel, and configured to reflect the light from the light source toward the display panel, the concave reflective sheet including a four-sided bottom face part with two pairs of mutually opposing sides (11B, 11C), two short edge-side side face parts (12) and two long edge side face parts (12) forming four side face parts of the concave reflective sheet; wherein a first peripheral portion extends from one of the sides of the bottom face part, and a second peripheral portion (12A, 12) has a first section (12) extending from adjacent one of the sides of the bottom face part that is adjacent to the one of the sides and a second section extending from the first section (12), the first peripheral portion and the second section of the second peripheral portion (12A, 12) partially overlapping with each other at a location between ends of the one of the sides of the bottom face part to form one of the side face parts of the concave reflective sheet, the first section (12) of the second peripheral portion (12A, 12) forming adjacent one of the side face parts of the concave reflective sheet that is adjacent to the one of the side face parts of the concave reflective sheet, wherein the concave reflective sheet comprises first perforations along which the concave reflective sheet is valley-folded to form the bottom face part, the pair of short edge-side side face parts (12), each formed along one of the two pairs of mutually opposing side of the bottom face part, and the pair of long edge-side side face parts (12), each formed along the other one of the two pairs of mutually opposing side of the bottom face part, the concave reflective sheet further comprises a first slit formed in the first peripheral portion and extending in a direction intersecting with the one of the sides of the bottom part wherein a predetermined portion of the second section on a first slit side of the second section overlaps a predetermined region of the first peripheral portion, and characterized in that the first slit has one end on the one of the sides of the bottom part and in that the concave reflective sheet further comprises a second slit extending from the one end of the first slit to the adjacent one of the sides of the bottom face part wherein a predetermined portion of the second section on a second slit side of the second section overlaps a predetermined region of the bottom face part. a display panel; a light source configured to emit light from a rear side relative to the display panel toward the display panel; and a concave reflective sheet disposed on the rear side relative to the display panel, and configured to reflect the light from the light source toward the display panel, the concave reflective sheet including a four-sided bottom face part with two pairs of mutually opposing sides (11B, 11C), two short edge-side side face parts (12) and two long edge side face parts (12) forming four side face parts of the concave reflective sheet; wherein a first peripheral portion extends from one of the sides of the bottom face part, and a second peripheral portion (12A, 12) has a first section (12) extending from adjacent one of the sides of the bottom face part that is adjacent to the one of the sides and a second section extending from the first section (12), the first peripheral portion and the second section of the second peripheral portion (12A, 12) partially overlapping with each other at a location between ends of the one of the sides of the bottom face part to form one of the side face parts of the concave reflective sheet, the first section (12) of the second peripheral portion (12A, 12) forming adjacent one of the side face parts of the concave reflective sheet that is adjacent to the one of the side face parts of the concave reflective sheet, wherein the concave reflective sheet comprises first perforations along which the concave reflective sheet is valley-folded to form the bottom face part, the pair of short edge-side side face parts (12), each formed along one of the two pairs of mutually opposing side of the bottom face part, and the pair of long edge-side side face parts (12), each formed along the other one of the two pairs of mutually opposing side of the bottom face part, the concave reflective sheet further comprises a first slit formed in the first peripheral portion and extending in a direction intersecting with the one of the sides of the bottom part wherein a predetermined portion of the second section on a first slit side of the second section overlaps a predetermined region of the first peripheral portion, and characterized in that the first slit has one end on the one of the sides of the bottom part and in that the concave reflective sheet further comprises a second slit extending from the one end of the first slit to the adjacent one of the sides of the bottom face part wherein a predetermined portion of the second section on a second slit side of the second section overlaps a predetermined region of the bottom face part.