PURPOSE: To enable dial-in connection by converting an extension selecting number to an arbitrary extension selecting number for night-time zone by providing a night-time switching control line for switching to dial-in connection for night-time zone.

CONSTITUTION: In the night-time zone, it is announced to an exchange 1 in advance which extension telephone set for night-time reception a call is connected to, and stored in an extension selecting number converting means 13. In the night-time zone, a PBX 20 transmits the night-time switching signal to a night-time switching control line 3. This night-time switching signal is received by a night-time switching signal storing means 12 of the exchange 1. In this case, since the extension selecting number converting means 13 stores the extension selecting number of the extension telephone set to be connected at night, the reception is announced to a dial-in connecting means 11. Thus, the dial-in connecting means 11 transmits the extension selecting number of the extension telephone set for night reception to the PBX 20 so as to call the extension telephone set for night reception.