There is provided a first unit which constitutes a point-to-multipoint communication system and is connected to communicate with each of a plurality of second units. The first unit includes a control signal extraction unit, a signal switching unit and a controller. The control signal extraction unit extracts first control signals respectively transmitted from the plurality of second units. The signal switching unit includes a switching circuit, and selects any one of the first control signals respectively received through individual signal transmission lines. The controller receives the first control signal selected by the signal switching unit, determines an allocation ID to be allocated to a second unit corresponding to the selected first control signal based on the initial identification information of the selected first control signal, and controls the determined allocation ID to be transmitted to the corresponding second unit.