According to one embodiment, a backlight device includes an optical controller, a light source, a first light guide module, a second light guide module, and a first member. The light source faces the optical controller. The first and second light guide modules are configured to guide light emitted by the light source toward the optical controller. The first member is placed in a traveling path of the light emitted by the light source. The first member is located near a joining portion at which the first light guide module and the second light guide module are joined to each other.