1. A design aiding device comprising: a first storing section that stores board data created for a board that is to be designed; a second storing section that stored part data created for a part to be designed and arranged on the board; and a processor that creates assembled model data, representing an assembled model that assumes arrangement of the part on the board, on the basis of the board data and the part data stored in the first storing section and the second storing section, respectively, wherein the processor comprises: a recognizing section that recognizes a mounting face of a part model defined by the part data, the mounting face being mounted on a board model defined by the board data; and an arrangement processing section that creates the assembled model data by arranging the part model on the board model on the basis of the mounting face recognized by the recognizing section.