PURPOSE: To provide an image processing apparatus having a triangular wave forming device simple in constitution, forming triangular waves of a plurality of cycles and capable of changing over them at high speed in a one-pixel unit.

CONSTITUTION: In an image processing apparatus comparing an inputted image signal with a reference signal (triangular wave) of a predetermined cycle to output a binarized image signal modulated in pulse width, a clock signal generating part 4 generating a clock signal of a predetermined cycle, a CR integration circuit 5 having a resistor and at least one condenser and inputting the clock signal to generate a reference signal having an inclined part and a condenser selection means 8 receiving a cycle determining signal for determining the cycle of the reference signal to change the synthetic capacity of the condenser in the CR integration circuit are provided. The synthetic capacity of the condenser is changed in the CR integration circuit at the time of the formation of a triangular wave to generate a plurality of reference signals different in cycle and a pulse width modulation signal corresponding to an image tone is outputted.