In a display device which adopts the digital system for expressing gray scales in 2^k unit, when gamma correction is performed so as not to generate omissions in the gray scales and display suitable for human visibility is further performed, it has been necessary to output a bit number several times the bit number of perceived luminance scale to be outputted in original intention in the real luminance scale. The invention suppresses the gamma value in gamma correction to such values as low as 2.0 or below (preferably 1.6 to 1.8). In addition, the invention uses a display device allowing 2^k gray scale display (nk2n) to perform 2ⁿ- a gray scale display (02ⁿ, is a natural number).