To provide a communication device capable of suppressing the frequency variation of an oscillator when transmission and reception are switched over.

A transmitter 300 operates in response to a signal from a VCO (Voltage Controlled Oscillator) 320, and has a plurality of transmitting circuits therein. A receiver 310 operates in response to the signal from the VCO 320, and has a plurality of receiving circuits therein. A transmitter BIAS 323 and a receiver BIAS 324 carry out a power source variation suppression process for suppressing time variation of a power source current of the transmitter 300 or the receiver 310 at least in any of cases of starting a transmission operation, stopping the transmission operation, starting a reception operation, and stopping the reception operation.