PURPOSE: To attain correct binarizing operation, by using a comparison signal which follows immediately when a facsimile signal changes from white to black level and follows after a prescribed time when the signal changes from black to white level.

CONSTITUTION: The anode of a diode 7 and a non-inverting input of a comparator 2 are connected to an input terminal 1, the cathode of the diode 7 is connected with an inverting input of the comparator 2, a resistor 8 and a capacitor 9, and a voltage V2 is impressed to the other end of the resistor and the capacitor 9. A comparison voltage impressed to the inverting input of the comparator 2 follows the facsimile signal immediately when the facsimile signal changes from the white to the black level, and follows after a prescribed time when the signal changes from the black to the white level.