To constitute a system device that connects a power supply and a plasma display through a junction cable so that, if the junction cable is disconnected, high-voltage power supply will be interrupted to eliminate the danger of electric shock.

Of the power supply input connectors 31 of a plasma display 3, the pin #1 is connected with the ground of the plasma display 3, and the corresponding pin #1 of the power supply output connectors 11 of a power supply 1 is connected with a detecting terminal for the judgment of whether a junction cable 2 is connected. The wires in the junction cable 2 is made to correspond to that so that it will be judged according to whether the detecting terminal is connected with ground whether to turn on power. Further, low- voltage power is first supplied to the plasma display 3, and, if current is passed through, then high-voltage power supply is actuated.