PURPOSE: To realize not only the centralized answer process but transfer process of the incoming calls for the slave stations via the attendant board at the master station, by providing the circuit which generates the hooking signal and converts the selection signal each at the master station.

CONSTITUTION: The master station possessing the attendant board 303 is connected to the slave stations via the interstation trunk line 108. Then the incoming call to the slave station is connected to the circuit 108 which is made previously to the memory device 107. Thus the call signal is transmitted 103 to the master station, and the board 303 performs an incoming display after detection 301 of the call signal. At the same time, the busy call of the circuit 108 is transferred to an optional extension telephone 109, and furthermore the hooking signal is generated 201 to be sent to the slave station. And the figure key information of the board 303 is converted 201 into the selection signal to be sent to the slave station. In this way, the incoming call to the slave station is sent to the board 303, and both the hooking signal and the selection signal are sent to the slave station from the master station. Then the incoming call to the slave station is connected to an optional extension within the slave station.