CAD pipe arrangement and pipe relationship database validation

An arrangement possible/impossible determination part of a piping order edit device: refers a pipe constituting a pipe list as a pipe subjected to determination; searches a main-branched pipe relationship database for a given pipe using identification information on the pipe subjected to determination as a search key; acquires a main pipe and a branched pipe corresponding to the searched given pipe; and, if there is a branched pipe positioned before the pipe subjected to determination in the pipe list or if there is a main pipe positioned after the pipe subjected to determination in the pipe list, the "arrangement possible/impossible" of the pipe subjected to determination is set at "impossible".