A plurality of hierarchy information management devices include a first hierarchy information management unit managing first hierarchy information in which information on instruments is represented in a hierarchy structure, and each hierarchy information management device manages the first hierarchy information of a different one of the instruments. A monitoring device includes: a second hierarchy information management unit generating second hierarchy information based on a plurality of different pieces of the first hierarchy information acquired from the hierarchy information management devices, the second hierarchy information being hierarchy information in which the first hierarchy information is connected in a hierarchy structure; a display unit displaying information; and a display processing unit performing a process of switching between a plurality of different monitoring screens for display on the display unit, the different monitoring screens corresponding to different layers in the second hierarchy information and showing the operating state of the monitoring targets.