PURPOSE: To prevent the setting of incorrect information due to noise by forming an interrupting means for interrupting noise generated from a setting means at the switching operation of an auxiliary power supply under OFF state of a power supply.

CONSTITUTION: An external adapter 200 is connected to a control device 100 for controlling a system through a connector 22. The control device 100 is constituted of a CPU 7, a non-volatile memory 5, a memory control circuit 6, an interface circuit 8 with the adapter 200, and a relay 1 for switching a power supply system. The adapter 200 is constituted of a switch 11, a display part 12, a switch/display part control circuit 10, a write/read control circuit 9, a load/unload switch 18, a battery 15, an output switch 4, and so on. Consequently, the relay 1 is turned to the battery 15 side at the OFF of the power supply and electric power is supplied from the battery 15 to respective circuits. The switch 18 is driven at the load/unload of the adapter 200 and the interface circuit 8 interrupts noise with an unstable level generated at the load/unload of the adapter 200 to prevent the setting of incorrect information.