To attain the automatic switching between the intra-office connection and the switchboard connection for a personal circuit.

A telephone set 5 is connected to an in-band ringer 20 via an exclusive line 102 of a PABX 1, and an E line 104 and an M line 105 of the PABX 1 are connected to a signal detector 7. The detector 7 detects the M line signal or the E line signal of an opposite station B and outputs the control signals 75 and 76 to input them to a circuit switch 6 which performs the switching between the exclusive line led from the PABX 1 or the exclusive line of the intra-office connection. The switch 6 is connected to the station B via a radio circuit 103.