A warp line is set directly on the surface of a virtual three-dimensional object model. A score set portion (22) configured to set scores for a virtual dress model formed within a 3-D space according to a manipulation instruction from the user to divide the virtual dress model into plural paper pattern regions R according to a manipulation instruction from the user, a warp line set portion (23) configured to set a warp line Lg for the paper pattern region R according to a manipulation instruction from the user, and a development portion (24) configured to form a virtual paper pattern by developing the paper pattern regions (R) into a 2-D plane in such a manner that the warp line Lg set by the warp line set portion (23) becomes linear, are included.