A first base station device (1, 1-1, 1-2) comprising: a wireless communication unit (102, 122, 142) that wirelessly communicates with a terminal device (21, 21-1), the wireless communication unit (102, 122, 142) receiving a predetermined signal from the terminal device (21, 21-1) in a state where the first base station device (1, 1-1, 1-2) is serving as a primary base station device communicating C-Plane data and a second base station device (2, 2-1, 2-2, 2-3) is serving as a secondary base station device communicating U-Plane data, the terminal device (21, 21-1) being configured to simultaneously communicate with the first base station device (1, 1-1, 1-2) and the second base station device (2, 2-1, 2-2, 2-3) using a C/U separation; and an execution unit (301, 401) that executes a handover between the first base station device (1, 1-1, 1-2) and the second base station device (2, 2-1, 2-2, 2-3) when the predetermined signal is received by the wireless communication unit (102, 122, 142), the handover being a handover in which the second base station device (2, 2-1, 2-2, 2-3) is switched from a secondary base station device to a primary base station device in a state where the second base station device (2, 2-1, 2-2, 2-3) is connected to the terminal device (21, 21-1) so as to be able to wirelessly communicate with the terminal device (21, 21-1), characterized in that the first base station device (1, 1-1, 1-2) is configured to not execute random access with the terminal device (21, 21-1) during execution of the handover; the first base station device (1, 1-1, 1-2) is configured to transmit to the second base station device (2, 2-1, 2-2, 2-3), identification information of the first base station device (1, 1-1, 1-2) as information of a candidate for a new secondary base station device during the handover between the first base station device (1, 1-1, 1-2) and the second base station device (2, 2-1, 2-2, 2-3), and the first base station device (1, 1-1, 1-2) is configured to connect to the terminal device (21, 21-1) as a secondary base station device after completion of the handover. a wireless communication unit (102, 122, 142) that wirelessly communicates with a terminal device (21, 21-1), the wireless communication unit (102, 122, 142) receiving a predetermined signal from the terminal device (21, 21-1) in a state where the first base station device (1, 1-1, 1-2) is serving as a primary base station device communicating C-Plane data and a second base station device (2, 2-1, 2-2, 2-3) is serving as a secondary base station device communicating U-Plane data, the terminal device (21, 21-1) being configured to simultaneously communicate with the first base station device (1, 1-1, 1-2) and the second base station device (2, 2-1, 2-2, 2-3) using a C/U separation; and an execution unit (301, 401) that executes a handover between the first base station device (1, 1-1, 1-2) and the second base station device (2, 2-1, 2-2, 2-3) when the predetermined signal is received by the wireless communication unit (102, 122, 142), the handover being a handover in which the second base station device (2, 2-1, 2-2, 2-3) is switched from a secondary base station device to a primary base station device in a state where the second base station device (2, 2-1, 2-2, 2-3) is connected to the terminal device (21, 21-1) so as to be able to wirelessly communicate with the terminal device (21, 21-1), characterized in that the first base station device (1, 1-1, 1-2) is configured to not execute random access with the terminal device (21, 21-1) during execution of the handover; the first base station device (1, 1-1, 1-2) is configured to transmit to the second base station device (2, 2-1, 2-2, 2-3), identification information of the first base station device (1, 1-1, 1-2) as information of a candidate for a new secondary base station device during the handover between the first base station device (1, 1-1, 1-2) and the second base station device (2, 2-1, 2-2, 2-3), and the first base station device (1, 1-1, 1-2) is configured to connect to the terminal device (21, 21-1) as a secondary base station device after completion of the handover.