A mobile communication system comprising: a first communication system, which includes: a user terminal that is present in a moving object; a first radio base station that is connected to the user terminal via a first radio interface and is provided in the moving object; and a first core network configured to be connected to an external network; and a second communication system, which includes: a radio mobile station that is connected to the first radio base station and provided in the moving object; a second radio base station that is placed along the path of movement of the moving object and connected to the radio mobile station via a second radio interface; and a second core network configured to be connected to the second radio base station and the first core network, wherein the radio mobile station is configured to receive lower layer data of user data transmitted from the user terminal on a first user plane between the user terminal and the first core network, to receive lower layer data of control signals transmitted from the user terminal on a control plane between the user terminal and the first core network, and to transmit the lower layer data of both the user data and the control signals on a second user plane that is provided between the radio mobile station and the second core network, and wherein the second core network is configured to receive lower layer data of user data transmitted to the user terminal on the first user plane, to receive lower layer data of control signals transmitted to the user terminal on the control plane, and to transmit the lower layer data of both the user data and the control signals on the second user plane. a first communication system, which includes: a user terminal that is present in a moving object; a first radio base station that is connected to the user terminal via a first radio interface and is provided in the moving object; and a first core network configured to be connected to an external network; and a user terminal that is present in a moving object; a first radio base station that is connected to the user terminal via a first radio interface and is provided in the moving object; and a first core network configured to be connected to an external network; and a second communication system, which includes: a radio mobile station that is connected to the first radio base station and provided in the moving object; a second radio base station that is placed along the path of movement of the moving object and connected to the radio mobile station via a second radio interface; and a second core network configured to be connected to the second radio base station and the first core network, a radio mobile station that is connected to the first radio base station and provided in the moving object; a second radio base station that is placed along the path of movement of the moving object and connected to the radio mobile station via a second radio interface; and a second core network configured to be connected to the second radio base station and the first core network, wherein the radio mobile station is configured to receive lower layer data of user data transmitted from the user terminal on a first user plane between the user terminal and the first core network, to receive lower layer data of control signals transmitted from the user terminal on a control plane between the user terminal and the first core network, and to transmit the lower layer data of both the user data and the control signals on a second user plane that is provided between the radio mobile station and the second core network, and wherein the second core network is configured to receive lower layer data of user data transmitted to the user terminal on the first user plane, to receive lower layer data of control signals transmitted to the user terminal on the control plane, and to transmit the lower layer data of both the user data and the control signals on the second user plane.