PURPOSE: To set the duty value of a PWM signal in accordance with the level of an analogue signal inputted from outside by converting cyclic digital data into a first analogue signal by means of a D/A conversion means and comparing the second analogue signal inputted from outside with the fist analogue signal in an output means.

CONSTITUTION: Cyclic digital data which is previously set based on cyclic digital data outputted from a binary counter 2 is outputted from a decoder 3. The output of the decoder 3 is converted into the cyclic analogue signal S1 by a D/A converter 4 and the analogue signal S1 is transmitted to an analogue comparator 5. The analogue signal S1 is compared with the analogue signal S2 inputted from outside in the analogue comparator 5, and a High or Low signal is outputted from the analogue comparator 5 according to whether the difference S1-S2 is positive or negative, whereby it turns into the PWM signal.