A multiplier core outputs a single-phase signal containing a frequency component having a frequency which is an even multiple of the frequency of input signals. A differential amplifier includes first and second nMOS transistors having respective source terminals connected to each other. The output signal from the multiplier core is inputted to the gate terminal of the first nMOS transistor, and the gate terminal of the second nMOS transistor is AC grounded. The differential amplifier differentially amplifies the signals inputted to the gate terminals of the first and second nMOS transistors to output a potential at the drain terminals of the first and second nMOS transistors as a differential signal. The output terminal of the multiplier core is connected through a series LC circuit to the source terminals of the first and second nMOS transistors.