Disclosed is a differential amplifier which comprises a differential pair comprising depletion-type first and second N-channel MOS transistors, a first current source that supplies a current for the differential pair, a current mirror circuit formed by transistor pairs connected in cascode fashion in two stages, for connecting an output pair of the differential pair in folded connection, second and third current sources connected to an input terminal of the current mirror circuit and an output terminal of the current circuit, respectively, and a buffer amplifier with that has an input terminal connected to the output terminal of the current mirror circuit and has an output terminal connected to an output terminal of the differential amplifier.