PURPOSE: To perform the overall remote maintenance of a system with a small number of devices by usually connecting an adapter that secures the electrical matching with a maintenance terminal to an automatic operation controller and switching the connection of the adapter to an information processor when this processor is driven.

CONSTITUTION: In a system halt state of a system, a power supply PW1 is applied only to an automatic operation controller AU and an information processor CP and peripheral devices U1...Un receive no supply of power. Under such conditions, a remote maintenance terminal RT is connected to a control part AR of the controller AU via an interface adapter LA and a changeover switch SWn. Thus the remote maintenance is possible with the controller AU including device equipments E1...En. When the controller AU applies a power supply PW2 according to a program and confirms that the processor CP is set under a workable state, the part AR activates a switch signal line C2 of the switch SWn to a processor DP to be diagnosed. When the DP is connected to the LA, the DP transmits not only the maintenance diagnosis information on the CP side but that on the AU side to the RT.