PURPOSE: To reduce output switching control terminals in number by forcibly applying a power voltage to the output terminal of an emitter follower circuit and then by using as a signal-path switching control signal the output of a comparison between the output level of the circuit and a reference voltage.

CONSTITUTION: With switch SW OFF, emitter follower transistor TrQ1 is in normal operation to obtain output VOUT. Then, this output is greater than the maximum level of an input signal and less than reference voltage Vref set smaller than a power voltage, so that TrQ2 and TrQ3 of a differential circuit will be ON and OFF respectively. The outputs of those TrQ2 and TrQ3 control a signal switching circuit (not shown in the figure) to transfer input signal Vinl to TrQ1. With switch SW ON next, output terminal P2 is forcibly held at power voltage Vcc; and TrQ1 is OFF to cut of an output signal and TrQ2 and TrQ3 are OFF and ON respectively to control a signal switching circuit, so that input signal Vinl will be transferred to another output circuit by switching while inhibited from being transferred.