A fabrication aiding apparatus capable of easily and properly setting a margin line is provided. The apparatus includes a RAM (Random Access Memory) to store three-dimensional shape data on a model of an abutment tooth to which a dental prosthesis is applied, an accepting section to accept the input of specification of an angle formed between a line defining a contact point and a reference axis on a face containing the reference axis in the model, a contact point detecting section to detect, based on the three-dimensional shape data, three-dimensional position information about a contact with the line forming a specified angle with the reference axis on the face containing the reference axis in the model, and a margin determining section to determine, based on coordinates of a contact point, three-dimensional position information of a margin line in the model.