PURPOSE: To provide a semiconductor integrated circuit device including a differential amplifier circuit which is made to selectively operate and reducing substantial power consumption.

CONSTITUTION: A signal detection circuit detecting whether the input signal of a differential amplifier circuit is a prescribed fixed level or not is provided. When the input signal is judged as the fixed level by the signal detection circuit, the operating current of the differential amplifier circuit is interrupted and the output level is made to the fixed level. A malfunction of a undesired circuit can be prevented and low power consumption can be realized corresponding to the interruption of the operating current by interrupting the operating current of the differential amplifier circuit and by setting the output signal in the fixed level since the substantial amplifier operation is not performed when the input signal of the differential amplifier circuit is the fixed level.