A lobby interphone of a doorphone system including the lobby interphone for a visitor to an apartment house to call residents of visiting places, room monitors for the residents to respond by receiving a call from the visitor, and distributors that relay between the lobby interphone and the room monitors, in which the lobby interphone is connected to a plurality of the room monitors with star-type wiring via two-wire cables and connected to one of the distributors via a two-wire cable, the distributors are connected to each other with daisy chain type wiring via two-wire cables, and each of the distributors is connected to the room monitors via two-wire cables, the lobby interphone comprising: a first terminal that is connected to one of the distributors; characterized in that the lobby interphone further comprises: a plurality of second terminals (T121, T122, T123, T124) that are connected to the plurality of room monitors with star-type wiring; a storage that associates key numbers allocated to the room monitors connected to the distributors with a number of the first terminal and stores the key numbers allocated to the room monitors connected to each of the second terminals (T121, T122, T123, T124) in association with numbers of each of the second terminals (T121, T122, T123, T124); a first relay unit that opens and closes a communication path with the distributors via the first terminal; a second relay unit that opens and closes a communication path with the room monitors via any one of the second terminals (T121, T122, T123, T124); and a controller that controls the first relay unit and the second relay unit so that a communication path with the distributor or the room monitor connected to a terminal (T121, T122, T123, T124) of which the number is associated with a key number included in an input signal is opened. a first terminal that is connected to one of the distributors; characterized in that the lobby interphone further comprises: a plurality of second terminals (T121, T122, T123, T124) that are connected to the plurality of room monitors with star-type wiring; a storage that associates key numbers allocated to the room monitors connected to the distributors with a number of the first terminal and stores the key numbers allocated to the room monitors connected to each of the second terminals (T121, T122, T123, T124) in association with numbers of each of the second terminals (T121, T122, T123, T124); a first relay unit that opens and closes a communication path with the distributors via the first terminal; a second relay unit that opens and closes a communication path with the room monitors via any one of the second terminals (T121, T122, T123, T124); and a controller that controls the first relay unit and the second relay unit so that a communication path with the distributor or the room monitor connected to a terminal (T121, T122, T123, T124) of which the number is associated with a key number included in an input signal is opened. a plurality of second terminals (T121, T122, T123, T124) that are connected to the plurality of room monitors with star-type wiring; a storage that associates key numbers allocated to the room monitors connected to the distributors with a number of the first terminal and stores the key numbers allocated to the room monitors connected to each of the second terminals (T121, T122, T123, T124) in association with numbers of each of the second terminals (T121, T122, T123, T124); a first relay unit that opens and closes a communication path with the distributors via the first terminal; a second relay unit that opens and closes a communication path with the room monitors via any one of the second terminals (T121, T122, T123, T124); and a controller that controls the first relay unit and the second relay unit so that a communication path with the distributor or the room monitor connected to a terminal (T121, T122, T123, T124) of which the number is associated with a key number included in an input signal is opened.