An object is to provide a liquid crystal display device having 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 103b that forms the optical sheet 134 of the backlight device 103 is made smaller than the opening for illumination Do in the diffusion region D, and the diffusion plate 103b is not provided in the vicinity of the end portions of the opening for illumination Do in the configuration. In this configuration, the reflection properties are different between in the vicinity of the end portions and the center portion of the opening for illumination Do, and the brightness increases in the vicinity of the end portions of the backlight device 103, so that an area in band form where the brightness is inconsistent can be prevented from being created in the end portions of the liquid crystal display device.