An operational amplifier including an input amplifier configured to amplify at least one differential input signal, a first common mode feedback amplifier configured to amplify a first common mode voltage, a cascode amplifier configured to cascode-amplify output signals from the input amplifier and the first common mode feedback amplifier, a first common mode voltage generator configured to generate a central voltage of the output signal from the cascode amplifier and input the central voltage to the first common mode feedback amplifier, and a frequency compensator configured to feedback the output signal of the cascode amplifier to the first common mode feedback amplifier so as to compensate a frequency of the first common mode feedback amplifier.