PURPOSE: To reduce an apparent picture noise at the time of A/D conversion by constituting an inexpensive A/D converter with a small number of bits in a picture having the comparatively low gradation such as a computer picture.

CONSTITUTION: The inputted picture signal from input terminals (R, G, B) 26-28 are A/D converted by first A/D conversion circuits 22-24, digital signals with values corresponding to a bright level by controlling switching circuits 34-36 when the values of the picture signal is smaller than the set value are outputted to output terminals (R, G, B) 37-39. When the A/D converted picture signals are larger than the set value, the A/D converted values are outputted as they are to the output terminals 37-39 by controlling the switching circuits 34-36. Thus, the flicker of the picture is reduced at the time of low brightness conspicuous by quantizing noises.