A CMOS differential operational amplifier has a fully differential structure to improve the output swing and a cascode amplification structure to improve the operating speed. This amplifier includes: a differential input stage 21 which receives differential input voltage signals and converts the input voltage signals into current signals; a cascode output stage 22 which amplifies the current signals from the differential input stage 21 and converts them into high gain output voltage signals; and a common-mode feedback circuit(CMF) 23 which makes a common-mode voltage signal of the output voltage signals equal to a reference voltage signal. To the output ports of the cascode output stage 22, a load capacitor (C.sub.L) 24 is connected.