A communication system comprises a main communication device including a first communication unit executing wireless communication by a first method (mainly for voice data communication) and a second communication unit executing wireless communication by a second method (for communication of data other than voice data at a higher transfer rate) and an auxiliary communication device (operating on a secondary battery) including first and second auxiliary communication units executing wireless communication with the first and second communication units by the first and second methods, respectively. Whether communication of data (except voice data) should be executed by the first method or by the second method is determined based on the amount of the data. When the first method is selected, the data is segmented in prescribed data units and the communication of the segmented data is executed by the first communication unit and the first auxiliary communication unit by the first method.