A SIP server generates a second call request for calling out group talk members corresponding to a first call request on the basis of the received first call request. Prior to transmitting the generated second call request to the group talk members, the SIP server transmits call request receiving information indicating that the first call request has been received. An SMS server transmits a start-up message to the group talk members on the basis of the received call request receiving information. The start-up message is used to start up an application which executes a group talk, and includes the member identification information of the group talk.