There is provided a high-frequency differential amplifier circuit comprising: a first MOS transistor, a second MOS transistor, a first positive feedback element and a second positive feedback element. The first MOS transistor and the second MOS transistor each has a source connected to a first power source and a drain connected through loads to a second power source. The first and second MOS transistors receives at their gates, first and second input signals having phases reverse to each other. The first positive feedback element includes a first capacitor and a first variable resistance connected in series between the gate of the first MOS transistor and the drain of the second MOS transistor. The second positive feedback element includes a second capacitor and a second variable resistance connected in series between the gate of the second MOS transistor and the drain of the first MOS transistor.