PURPOSE: To display the picture displayed on the display device of a process computer on the display device of an engineering work station through a WAN by suppressing the changes of the hardware and software of the process computer.

CONSTITUTION: The information about the facility of a power system is preserved in a preserving section 32 which preserves the information about the state of a power system through a collecting means 31 which collects the information about the power system. A one-line wiring diagram displaying means 33 edits the preserved information and an ESC command converting and outputting means 34 converts the edited information into ESC commands which can be displayed on a display device 7. A LAN transmitting means 35 converts the ESC commands into codes to be transmitted to a LAN. An information system 5 is constituted of a one-line wiring diagram displaying means 51 which reconverts the data received from the LAN into data which can be displayed on a display means 6 and one-line wiring diagram data storing section 52 which stores the reconverted data.