A server causes an information terminal device to display a selection image for allowing an operator to select a desired operation among one or more operations and a desired master device among one or more master devices based on operation request information stored in a first database and master device information stored in a second database. The information terminal device sends to the server a selection instruction of the operator who selects the desired operation and the desired master device via the selection image. The server receives an operation order acceptance of the operator by storing, in an operation plan database, an operator ID, a master device ID and the operation designated by the selection instruction in combination with one another.