PURPOSE: To obtain a desired characteristic by providing a variable current value constant current circuit as the means which discharges the electric charge accumulated in the base of a transistor TR in an output stage.

CONSTITUTION: When the base of a TR 1 with a Schottky barrier diode is in the low level, TRs 1 and 4 with Schottky barrier diodes are turned off because of a lack of Vbe, but a current flows to a TR 6 of the constant current circuit, and the electric charge accumulated in the base of the TR 4 with the Schottky barrier diode is discharged, and the output of an output terminal 32 goes to a high level of TTL. The resistance value of a variable resistor 20 is changed to change the current value of a TR 6, and thereby, the output duty and the rise characteristic are adjusted, and the high level potential of the output is adjusted.