A request destination management table that stores therein a service ID uniquely identifying a service being interrelated with a request destination to which execution of a service is requested and a report destination management table that stores therein a call ID uniquely identifying a call being interrelated with a report destination of a call state transition report indicative of state transition of the call are provided. An IP telephone receives a request for a supplementary service, obtains a request destination corresponding to a service ID of the supplementary service from the request destination management table, and transfers the request for the supplementary service to the request destination. The IP telephone receives a call state transition report, obtains a report destination corresponding to a call ID of the call state transition report from the report destination management table, and transfers the call state transition report to the report destination.