A design support device used to design a part in string or belt form, including: a part editing unit configured to edit a part by changing a position of a pass point through which the part passes; and a section comparison unit configured to compare a section having a plurality of consecutive pass points before the edition by the part editing unit with the sections after the edition by the part editing unit, and extracting the section in which relative positions or relative passing directions are different between two pass points in the sections.