A communication method includes determining a difference state of identification numbers of communication providers corresponding to a plurality of relay transfer apparatuses on a passing outward path to an opposing communication apparatus and on a passing return path from the opposing apparatus; and switching a first virtual communication channel set between intranets and a second virtual communication channel set between the intranets to dynamically substitute and use a first communication mode of transmitting and receiving encrypted communication data to and from the opposing apparatus through the first virtual communication channel and a second communication mode of transmitting and receiving plain text communication data to and from the opposing apparatus through the second virtual communication channel, according to the determination of the difference state of the identification numbers of the providers.