PURPOSE: To allow one and same chip to be compatible with two kinds of frequencies or over.

CONSTITUTION: A logic processing section J2, logic level decision circuits E2, F2 and a constant current circuit A2 are formed by ECL configuration. A current given to the logic processing section J2 by the constant current circuit A2 and the resistance of the resistor in the logic level decision circuits E2, F2 are simultaneously switched by a control signal S. When a frequency of an input signal is high, the constant current circuit A2 supplies a large current and the logic processing section J2 is connected to a power supply VCC through a smaller resistance of the resistor in the logic level decision circuits E2, F2. Thus, the input signal with the high frequency is processed in an excellent way while keeping the same amplitude as that of the input signal with the low frequency.