An end-to-end delay acquisition unit in a radio terminal measures end-to-end delay time, which is the delay time required for end-to-end transmission and reception, by using PING packets in an IP network or the time stamp function of RTCP during VoIP communication. An activation period modification determination module that is provided in the radio terminal modifies the activation period of the radio communication module that carries out radio communication such that the end-to-end delay time that has been measured by the end-to-end delay acquisition unit is equal to or less than a standard value that has been stipulated in advance.