PURPOSE: To provide a telephone system capable of stably providing every kind of service even when the status of a room is changed.

CONSTITUTION: When an incoming call arrives at a trunk line 1, a main device 10 sends an incoming call signal to a unit device 30. The unit device 30 generates a incoming call signal by the signal. The control part of the unit device 30 sends information representing a response to the main device 10 by a response signal from a remote control unit 30A, and also, opens a speaker line and a microphone line. The main device 10, when receiving the information, connects the trunk line 1 to the unit device 30. The control part of the unit device 30 sends the information representing a simultaneous call from the remote control unit 30A to the main device 10 by such simultaneous call, and also, opens the speaker line. The main device 10, when receiving the information, sends a call signal to each of the unit devices 30, 40.