1. A display device for displaying a first image in a first direction and a second image in a second direction different from the first direction, the display device comprising: a display panel having a plurality of pixels arrayed in a matrix, the plurality of pixels including a first pixel which is any one of pixels, a second pixel adjacent to the first pixel, a third pixel adjacent to the first pixel opposite from the second pixel, and a fourth pixel adjacent to the second pixel opposite from the first pixel; a backlight configured to emit a light to a back surface of the display panel; and a parallax barrier made of a light shielding material and formed on a front surface of the first pixel and the second pixel, the parallax barrier including an opening having no light shielding material at a boundary portion between the first pixel and the second pixel, the parallax barrier configured so that a light from the first pixel passes through the opening of the parallax barrier and is emitted to the first direction, and a light from the second pixel passes through the opening of the parallax barrier and is emitted to the second direction, at least part of a light emitted from the backlight and entered the boundary portion between the first pixel and the second pixel passes through the opening of the parallax barrier, at least part of a light emitted from the backlight and entered a boundary portion between the first pixel and the third pixel passes through the opening of the parallax barrier, and at least part of a light emitted from the backlight and entered a boundary portion between the second and the fourth pixel passes through the opening of the parallax barrier, so that a luminance of the first image when the first image and the second image are black images is increased to satisfy a following formula (1) 
 ( B−A )/ A≦ 1  Formula (1) wherein A represents the luminance of the first image when the first image and the second image are black images, and B represents a luminance of the first image when the first image is a black image and the second image is a white image.