A CAD file converting device for applying CAD files created in a CAD system for machines to a CAD system for ships maps modeling units that the CAD files created in the CAD system for machines and those applied in the CAD system for ships, and converts parameter values determining feature shapes in the mapped modeling units into parameter values proper to the CAD files of the CAD system for ship design. Accordingly, CAD files of a CAD system for machines can be accurately converted into CAD files of a CAD system for ships.