An on-site system building support tool for assisting a user in building an on-site system by displaying a layout creation screen having an icon area for displaying icons, each of which represents any of various kinds of machines that can be used, and a canvas area in which a virtual system is built. The icons are displayed in the canvas area and connected to each other through an association line. A model setting screen is used to display the icons, and on the basis of setting conditions displayed on the model setting screen, a load on the virtual system built on the canvas area is calculated and displayed which applies to the environment. This enables checking of an environmental load on the basis of various kinds of conditions of the site.