PURPOSE: To display the use condition of a facsimile without providing a special button by using the line wire button of a private telephone set and displaying the effect when the communication content of each line wire is the facsimile communication.

CONSTITUTION: When a line wire (a) starts to use, the prescribed signal is sent to a line wire button 8a corresponding to a private telephone set 2 and a light emitting diode 9a is light-emitted. At this time, when a special signal CED to show that a frequency detecting means 7 is the facsimile communication, or a CNG signal is detected, a signal to show that the facsimile communication is performed is sent to the private telephone set 2, a light emitting diode 9b in the line wire button 8a is light-emitted, and the line wire (a) displays that the facsimile communication is performed. When the channel to the line wire (a) is formed and a CED signal to show that the facsimile communication is performed or a CNG signal is not detected, a signal to show that the facsimile communication is not performed is sent to the private telephone set 2 and a light emitting diode 9c in the line wire button 8a is light-emitted.