A method for manufacturing a three-dimensionally shaped plastic object comprising: a laminating process to form a powder layer by supplying powder material; and a sintering process to radiate a light beam or an electron beam to the powder layer and move a location radiated by the light beam or the electron beam to sinter the powder layer, wherein the laminating process and the sintering process are configured to alternately repeat, and wherein the sintering process for a respective powder layer comprises: setting a vector molding path for scanning a region to be molded along a contour thereof by the light beam or electron beam, wherein the vector molding path is a continuous route formed in an endless ring along the contour of the region to be molded; and setting a raster molding path for scanning an inner region of the region to be molded by the light beam or electron beam so as to hatch the mentioned region, wherein the raster molding path is a continuous route which does not pass the same line and does not form any intersection, wherein between two adjacent straight lines or curve lines of the raster molding path, a distance is set to be larger than a radiation diameter of the light beam or the electron beam and smaller than 10 times of the radiation diameter. a laminating process to form a powder layer by supplying powder material; and a sintering process to radiate a light beam or an electron beam to the powder layer and move a location radiated by the light beam or the electron beam to sinter the powder layer, wherein the laminating process and the sintering process are configured to alternately repeat, and wherein the sintering process for a respective powder layer comprises: setting a vector molding path for scanning a region to be molded along a contour thereof by the light beam or electron beam, wherein the vector molding path is a continuous route formed in an endless ring along the contour of the region to be molded; and setting a raster molding path for scanning an inner region of the region to be molded by the light beam or electron beam so as to hatch the mentioned region, wherein the raster molding path is a continuous route which does not pass the same line and does not form any intersection, wherein between two adjacent straight lines or curve lines of the raster molding path, a distance is set to be larger than a radiation diameter of the light beam or the electron beam and smaller than 10 times of the radiation diameter. setting a vector molding path for scanning a region to be molded along a contour thereof by the light beam or electron beam, wherein the vector molding path is a continuous route formed in an endless ring along the contour of the region to be molded; and setting a raster molding path for scanning an inner region of the region to be molded by the light beam or electron beam so as to hatch the mentioned region, wherein the raster molding path is a continuous route which does not pass the same line and does not form any intersection, wherein between two adjacent straight lines or curve lines of the raster molding path, a distance is set to be larger than a radiation diameter of the light beam or the electron beam and smaller than 10 times of the radiation diameter.