A liquid crystal display device has a thin structure with a backlight device appropriate for illuminating a liquid crystal panel where there is no area in band form where the brightness is inconsistent. The size of the diffusion plate that forms the optical sheet of the backlight device is made smaller than the opening for illumination in the diffusion region, and the diffusion plate is not provided in the vicinity of the end portions of the opening for illumination in the configuration. In this configuration, the reflection properties are different in the vicinity of the end portions and as the center portion of the opening for illumination, and the brightness increases in the vicinity of the end portions of the backlight device, so that an area in band form where the brightness is inconsistent can be prevented from being created in the end portions of the display device.