ASK modulation apparatus and method

A base band signal is frequency limited by a band limiting circuit 1. The waveform of this output signal rises and falls smoothly against a time axis. A driving circuit 2 functions as a buffer amplifier with voltage gain of 1 between the band limiting circuit 1 and ASK modulation circuit 3, and the output voltage wave is equal to the output waveform of the band limiting circuit 1. The ASK modulation circuit 3 turns on/off a field effect transistor 61 by the output signal voltage from the driving circuit 2, thereby discontinuing the carrier of the microwave band to be externally entered and performing ASK modulation (binary ASK), and provides a desired ASK modulated waveform as a result.