A radio communication system comprising: a first base station configured to operate a first cell; at least one second base station, each of which is configured to operate a second cell; a core network including a mobility management apparatus and a data transfer apparatus; and a mobile station having a capability to establish a data radio bearer in the second cell when the mobile station has established a signaling radio bearer in the first cell, wherein the first base station is configured to: receive, from the mobile station through the signaling radio bearer, a signal containing a NAS message that causes a setup of a data bearer in the data transfer apparatus; send, when forwarding the NAS message to the mobility management apparatus, a control message that causes a suspension of the setup of the data bearer to the mobility management apparatus, and send, after sending the control message, a setup request for setting up the data bearer to the mobility management apparatus, wherein the first base station is further configured to receive measurement information regarding the at least one second base station from the mobile station, and select, from the at least one second base station, a selected base station to terminate the data bearer, and the setup request contains base station information indicating the selected base station that has been selected from the at least one second base station. a first base station configured to operate a first cell; at least one second base station, each of which is configured to operate a second cell; a core network including a mobility management apparatus and a data transfer apparatus; and a mobile station having a capability to establish a data radio bearer in the second cell when the mobile station has established a signaling radio bearer in the first cell, wherein the first base station is configured to: receive, from the mobile station through the signaling radio bearer, a signal containing a NAS message that causes a setup of a data bearer in the data transfer apparatus; send, when forwarding the NAS message to the mobility management apparatus, a control message that causes a suspension of the setup of the data bearer to the mobility management apparatus, and send, after sending the control message, a setup request for setting up the data bearer to the mobility management apparatus, wherein receive, from the mobile station through the signaling radio bearer, a signal containing a NAS message that causes a setup of a data bearer in the data transfer apparatus; send, when forwarding the NAS message to the mobility management apparatus, a control message that causes a suspension of the setup of the data bearer to the mobility management apparatus, and send, after sending the control message, a setup request for setting up the data bearer to the mobility management apparatus, wherein the first base station is further configured to receive measurement information regarding the at least one second base station from the mobile station, and select, from the at least one second base station, a selected base station to terminate the data bearer, and the setup request contains base station information indicating the selected base station that has been selected from the at least one second base station.