The backlight device is configured in a planar geometry by the combination of a plurality of light emitting units. The light guide plate of the light emitting unit has a light guide unit that guides light from the light source and a light emission surface that emits light from the light guide unit. Adjacent light emitting units are arranged to cross to each other and the light emission surface of a light emitting unit overlaps with the light guide unit of another light emitting unit such that the light guide unit of each light guide plate of the light emitting unit does not extend outside the light emission region of the backlight device.