The present invention enables support of a process for creating a detailed layout design which takes construction into account, and contributes to a reduction in the workload of the layout design process. A layout editing unit causes an interface unit to display a layout design data editing screen, receives an edit instruction input onto the screen, and edits the layout design data in accordance with the edit instruction. The layout editing unit classifies the layout design data into five data types, namely building data, equipment arrangement data, equipment connection element data, equipment connection path data, and user-specified range data, and edits the data of each data type individually. A storage unit stores the editing results of the layout design data. A CAD conversion unit converts the layout design data into a two-dimensional CAD drawing or a three-dimensional CAD model, and causes the interface unit to display the two-dimensional CAD drawing or three-dimensional CAD model on a screen.