PURPOSE: To stop a print letter to a prescribed position by constituting a feedback loop by a time constant circuit, inverting a phase of an output voltage of an operational amplifier so as to feed it back to a non-inverting input and obtaining an output signal at a maximum value of an input voltage.

CONSTITUTION: The operational amplifier 10 is provided to each of compartors 8, 9, a reference voltage Vref is inputted to the non-inverting input terminal of the amplifier 10 while dividing the voltage by resistors R2, R3 and each of input voltages Vi1, Vi2 is inputted to an inverting input. Each amplifier 10 is provided with a feedback loop constituted by a time constant circuit comprising a capacitor C and a resistor R1 and this feedback loop is connected to the non-inverting input of the amplifier 10. Further, each of output voltages V1, V2 of the amplifier 10 is inverted by a transistor TR1 and fed back to the non-inverting input of the amplifier 10 via a resistor R4. Then the changeover timing of the input voltages Vi1, Vi2 is adjusted so as to output an output signal close to the maximum value of the input voltage thereby stopping the print letter to a prescribed position.