A communication restriction is performed in an appropriate manner for a mobile station (subscriber) that has roamed out of a communication operator's network where subscriber information is registered into another one. In a roaming system including an HLR 110 and a GGSN 120 of a first communication operator's communication network 100 and an SGSN 220 of a second communication operator's communication network 200, the SGSN 220 receives a packet transmission request from a mobile station 210 and transfers it to the GGSN 120. The GGSN 120 that has received the transferred packet transmission request makes an inquiry about subscriber information of the mobile station 210 to the HLR 110. The HLR 110 identifies whether or not the packet transmission request is to be subject to a restriction, and returns an identification result to the GGSN 120 when it is to be subject to the restriction. The GGSN 120 transfers a response to the identification result to the SGSN 220. The SGSN that has received the transfer transfers the response to the identification result to the mobile station 210.