A control station apparatus (60, 20) being configured in a core network and connecting a Packet Data Network, PDN, with the core network, the control station apparatus (60, 20) comprising: a transmission/reception portion configured to: transmit/receive a first flow and a second flow by using a first communication path connecting a mobile station apparatus and the core network via a first access network, the first communication path being established based on an Access Point Name, APN, and transmit, toward the mobile station apparatus via a second gateway, a control message containing at least an identification information of the first flow, in order to switch communications of the first flow to use a second communication path connecting the mobile station apparatus and the core network via a second access network, the second communication path being established based on the APN, the second gateway being connecting the core network and the second access network, receive, from a direction of the mobile station apparatus, a response control message for the control message, and after reception of the response control message, transmit or receive the first flow by switching to use of the second communication path based on the control message, wherein the control message is a message transmitted in a procedure initiated by the core network, the procedure being to change a communication path for the first flow. a transmission/reception portion configured to: transmit/receive a first flow and a second flow by using a first communication path connecting a mobile station apparatus and the core network via a first access network, the first communication path being established based on an Access Point Name, APN, and transmit, toward the mobile station apparatus via a second gateway, a control message containing at least an identification information of the first flow, in order to switch communications of the first flow to use a second communication path connecting the mobile station apparatus and the core network via a second access network, the second communication path being established based on the APN, the second gateway being connecting the core network and the second access network, transmit/receive a first flow and a second flow by using a first communication path connecting a mobile station apparatus and the core network via a first access network, the first communication path being established based on an Access Point Name, APN, and transmit, toward the mobile station apparatus via a second gateway, a control message containing at least an identification information of the first flow, in order to switch communications of the first flow to use a second communication path connecting the mobile station apparatus and the core network via a second access network, the second communication path being established based on the APN, the second gateway being connecting the core network and the second access network, receive, from a direction of the mobile station apparatus, a response control message for the control message, and after reception of the response control message, transmit or receive the first flow by switching to use of the second communication path based on the control message, wherein the control message is a message transmitted in a procedure initiated by the core network, the procedure being to change a communication path for the first flow.