A telescopic differential operational amplifier circuit for use in a pipelined A/D converter is provided with two auxiliary differential amplifiers connected to two cascode circuits, each including cascode-connected first to fourth transistors. During the sampling phase, first and second switches are turned on to apply a predetermined bias voltage to the gates of first and fourth transistors, and the input terminal of the differential operational amplifier circuit is set to a common mode voltage. During the hold phase, the first and second switches are turned off so that a voltage of each of the gates of the first and fourth transistors change to follow an input signal inputted via the input terminal with coupling capacitors operating as a level shifter of the input signal. Then the differential operational amplifier circuit performs push-pull operation operative only in a transconductance drive region, and is prevented from operating in a slewing region.