A method of creating a three-dimensionally shaped object, the method having: a creation step for creating image data for printing an image on a thermally expandable sheet; a printing step for printing an image on the thermally expandable sheet on the basis of the image data created in the creation step; and a protuberation step for partially protuberating the thermally expandable sheet via thermal expansion by irradiating light toward the image printed on the thermally expandable sheet in the printing step. The creation step creates image data such that a grayscale of an image is set so that a fastening portion that fastens a thermally expandable sheet is either intermittently or continuously surrounded by a region where a protuberation height resulting from the thermal expansion is high.