PURPOSE: To achieve an automatic connection of a tester to the control center while automatically indicating the state and results of the testing by transmitting the contents of a development connection diagram to the tester through the transmission of information utilizing a computer.

CONSTITUTION: A main circuit load terminal 14, a control circuit terminal 15 and a test circuit switch 10 are connected to a control center 8 with a main circuit power source unit 9 and a connection cable 12. A testing circuit forms a voltage withstand testing circuit and a sequence testing circuit with a circuit changeover switch 16 and the selection is made by a tester's operation. When the voltage withstand testing circuit position is selected and operated, a circuit selection repeater 21 fails to work and the control center 8 is connected to the voltage withstand tester 11 to enable the execution of a voltage withstand testing. When the sequence testing circuit position is selected and operated, the circuit selection repeater 21 works the control center 8 is connected to a circuit composer 6. The circuit composer 6 operates a circuit composition repeater 23 by information on connection in the design to compose a circuit which is connected to an external equipment provided on a sequence tester 7.