Such internal decoration is implemented that an object looks a target color as viewed in any direction, and that the object is colored and has image depiction in any cross-section. A method is provided for producing a three-dimensional object by extruding a build material to form a layer corresponding to each of cross-sections obtained by slicing a target object by a plurality of parallel planes, and depositing such layers in sequence so as to form the three-dimensional object. A white material 15 and one or two or more decoration materials 13 of colors other than white, which solidify wider a predetermined condition after extruded from nozzles, are used as the build material. The decoration materials 13 and the white material 15 are mixed to form the layer.