A signal modulator that can control transmission power if level adjustment of a continuous signal from an oscillator is executed is provided. A pulse generator of one example of a signal modulator includes an oscillator, a control signal generator, a multiplier, a filter, and a control section. The oscillator and the multiplier are active circuits formed of active elements. A continuous signal is output from the oscillator and is input to the multiplier and the multiplier intermittently operates by a control signal output from the control signal generator, whereby a pulse signal is generated and the power level is easily adjusted by a signal from the control section.