A communication device has a transmission/reception unit and a communication processing unit. The transmission/reception unit is configured to conform to a plurality of communication methods. The communication processing unit selects one of the plurality of communication methods with respect to each time slot based on device time in accordance with a predetermined selection rule, to perform communication via the transmission/reception unit by the selected communication method. In time synchronization master processing, a first communication device gives device time of the device itself as a time stamp to a time synchronization request signal and transmits the time synchronization request signal. In time synchronization slave processing, a second communication device receives the time synchronization request signal and calibrates the device time of the device itself based on the time stamp in the time synchronization request signal.