An amplitude modulator comprises: a signal processing section for receiving a source signal for wide bandwidth use, splitting the source signal into two source signals for lower frequency use and for higher frequency use, respectively, signal processing the two source signals individually, and outputting a lower-frequency-use source signal and a higher-frequency-use source signal; a first modulation section for modulating the lower-frequency-use source signal and outputting a lower-frequency-use modulation signal; a second modulation section for modulating the higher-frequency-use source signal and outputting a higher-frequency-use modulation signal; a synthesis output section for inputting the lower-frequency-use modulation signal to a first input terminal, the input thereof causing extraction of only a lower-frequency component, for inputting the higher-frequency-use modulation signal to a second input terminal, the input thereof causing extraction of only a higher-frequency component, for synthesizing the higher-frequency component and the lower-frequency component, and for outputting a modulated signal corresponding to the source signal for wide bandwidth use, to a next step.