To provide a signal generator where the impedance after a mixer is unchanged even when an output terminal connects directly to the mixer for receiving an output of a voltage controlled oscillator VCO as one input signal.

A signal generator 5 is provided with a voltage controlled oscillator 2 that gives either of two input signals to a frequency mixer circuit 1 that provides an output of a signal with a frequency being a difference between or a sum of both the signals, an attenuation circuit 6 placed between the voltage controlled oscillator 2 and the frequency mixer circuit 1 and attenuates an output signal of the voltage controlled oscillator, and a filter circuit 7 that limits a frequency band of the output signal of the attenuation circuit.