When a signal of a double frequency is generated from the original signal, conventionally a 90-degree phase-shift circuit is necessary to suppress an output of a DC component and efficiently obtain a double wave. According to the present invention, an equal RF signal is inputted to input terminals and an output is matched with a frequency as high as that of the original frequency in a Gillbert cell double-balanced mixer, so that a doubled output is obtained with no DC offset. According to the circuit configuration of the present invention, it is possible to provide a circuit readily performing integration and to efficiently output only a double frequency merely by inputting a simple differential signal without the need for the original signal which has been phase controlled. Further, a DC short circuit in the resonance circuit makes it possible to eliminate a DC offset voltage in an output.