PURPOSE: To execute a control of an exchange and a test of a trunk from a trunk test board by executing a transfer of an information or a selection of a trunk testing circuit to a main control device of the exchange by an information sent out of the trunk test board.

CONSTITUTION: In case of executing a blocking of a trunk T-A6 of an exchange A from a trunk test board 1, a trunk testing device 2 is called, and a blocking information is sent by connecting the test board 1 to T-A1 of the device 2. In the device 2, a selecting circuit 3 selects an interface circuit 4, and a controlling circuit 5 transfers a blocking information of T-A1 to a transmission control device 6 through the circuit 4. A main control device 7 of a switchboard detects an information sent to the device 6 and blocks T-A6. Subsequently, when a designated information of T-A6 and a number of a test trunk TT of an exchange B are sent out of the test board 1, the circuit 3 selects a trunk testing circuit 8. The circuit 8 sends out the designated information of T-A6 and the number of the trunk TT. The device 7 connects T-A4 and T-A6, sends the number of TT to the exchange B and connects it to TT, and executes a test of the test trunk TT.