To provide a service customized for each user and for each application, when user host terminal H1 communicates with user host terminal H2 using VoIP, the terminal H1 transmits a service initiation message to service execution units SN1 and SN2. By this message, the service execution unit SN1 and SN2 require service information L-SPC (A) and service information G-SPC (A), both information regards to VoIP service of the term H1, to authentication server A1 respectively. The service execution unit SN1 and SN2 execute a service based on L-SPC (A) and G-SPC (A) respectively. Doing this, service execution unit may provide a service customized for each user and for each application.