PURPOSE: To use stably a capacitance of an MOS capacitor by using a gate- source capacitor of an MOS transistor so as to apply always a bias voltage to the MOS capacitor.

CONSTITUTION: A signal adding a voltage VB of a bias voltage generating section E to an output signal of an operational amplifier is fed to other terminal of the MOS capacitor CM1 whose gate is connected to an inverting input of the operational amplifier. Switches S1, S2 are operated respectively in phase. Then the voltage across the MOS capacitor is used to be larger than a threshold voltage VTH. Thus, even when the voltage across the capacitor is changed, the capacitance is unchanged and a stable phase inverting integration device is offered without using any special floating capacitor.