Provided is a backlight device which can suppress a damage of a display panel or a diffusion sheet while suppressing the size of the device. The backlight device (20) includes: a diffusion sheet (25); and a support member (31) having a support plane (31a) for supporting the diffusion sheet and arranged below the diffusion sheet. The diffusion sheet has a center of gravity (G1) set at the arrow C direction, i.e., at the side opposite to a liquid crystal display panel (12) as compared to a contact position (tip end (P1)) between the lower surface (25d) of the diffusion sheet and the support plane of the support member when the diffusion sheet is not warped.