PURPOSE: To prevent deterioration in picture quality, and to transmit an encoded signal efficiently to a receiving terminal, by discriminating between a binary density image and a half-tone image on an original, and performing the best encoding regarding picture signals which correspond to respective picture.

CONSTITUTION: A picture signal from an image signal input terminal 1 is converted by an A/D converter 2 into a 4-bit digital signal of every picture element, which is stored in a 1-line shift register 3 as much as one line. The output of this register 3 is applied to a mean variance calculator 8 and supplied to a shift register 4. At the same time, the output of the shift register 4 is applied to shift registers 5∼7 successively. The outputs of the respective registers 4∼7 are applied to the calculator 8, and the output of the register 5 is applied to a delay circuit 11. The calculator 8 calculates the average and variance of the picture signal of each input picture element, and those results are applied to a discriminating circuit 9 to discriminates between a binary density picture and a half- tone picture with regard to the picture element; and 1 for the half-tone picture or 0 for the binary density image is supplied to an output terminal 10.