In a communication system, one of a plurality of communication apparatuses that acts as a host controls data transmission and the other communication apparatuses that act as devices perform data transmission under control of the host over a predetermined communication interface. The communication apparatuses have both host and device roles, and are configured to exchange the host and device roles by using a predetermined communication protocol are connected to the predetermined communication interface. A first apparatus acts as a host and a second apparatus as a device. The second apparatus transmits information concerning the second apparatus to the first apparatus. The first apparatus compares the transmitted information with information concerning the first apparatus to determine whether or not to switch the host and device roles according to a predetermined criterion. In response to an affirmative determination, the host and device roles are switched by using the predetermined communication protocol.