To faithfully engrave on a line drawing original image an intaglio drawing line having an accurate depth value, a cross section shape of a desired drawing line, and a padding shape, by generating engraving data for an NC machining tool from the line drawing original image made on base material.

A line drawing pattern drawn on the base material such as paper is image-inputted by using an image input unit, and bit map data is obtained. Thereafter, image processing such as an outline trace is applied to the bit map data, and line drawing data of a vector data type are obtained. Cutter paths for the NC machining tool are prepared by carrying out shrinkage processing with respect to the line drawing data a plurality of times. Text processing for imparting a desired depth value or the like to each cutter path prepared is carried out to make the engraving data for the NC machining tool of four-axis control. An intaglio drawing line forming body is engraved on the base material such as metal based on the data.