To provide an operational amplifier short in calibration time without generating shock noise before and after a self calibration operation.

In this operational amplifier, by cutting off a voltage amplifier 106 constituting the operation amplifier and a capacitor 109 and a current amplifier 110 by an analog switch 107 at the time of self calibration and short- circuiting both input terminals of the voltage amplifier by the analog switch 105, the output of the voltage amplifier is turned to an offset voltage, an offset adjustment part inside the voltage amplifier is adjusted corresponding to the value and an offset is reduced. Since the voltage of the input terminal of the current amplifier is held by the capacitor, the change of the voltage of the input terminal of the current amplifier before and after the self calibration is small and the large shock noise is not generated at an output terminal 111. Also, since the capacitor is cut off from the voltage amplifier and becomes unrelated to a calibration operation, the voltage amplifier obtains a desired voltage amplification factor at a high frequency and the calibration time is shortened.