PURPOSE: To clearly reproduce the half tone of a picture or a photograph and to reproduce even a fine character while emphasizing the edge of the character by changing a reference signal for expressing the half tone according to the contents of an image signal to be binarized.

CONSTITUTION: The image signal to be binarized is inputted and simultaneously, an image separating circuit 2 discriminates a part being binarized at present is the picture, photograph or character. According to the discriminated result, the circuit 2 changes over a switch 5 to the side of a terminal 11 in the case of the character and changes over the switch 5 to the side of a terminal 12 in the case of the picture or the photograph. Namely, in the case of the character, the contour of the character is emphasized so as to clearly observe even the small character by strengthening the edge emphasis while remaining gradation at a certain degree by impressing the image signal through a first CR circuit to the reference signal. In the case of the picture or the photograph, the image signal is impressed through a second CR circuit to the reference signal, the edge emphasis is weakened, and the picture or the photograph is clearly observed by expressing the half tone according to a dither pattern applied as the reference signal.