1. A numerical control (NC)-program searching method comprising: generating, when shape data of a machining target is input from an outside, image data corresponding to the shape data of the machining target as machining target image data; generating, based on NC programs created in the past, image data of a machining finish shape as finish shape image data; storing the finish shape image data in association with an NC program corresponding thereto; comparing the machining target image data and the finish shape image data to thereby calculate a similarity of the machining target image data to the finish shape image data; searching, based on the similarity, candidates of finish shape image data similar to or matching the machining target image data and displaying the candidates; displaying, out of the candidates of the finish shape image data, an NC program for finish shape image data designated by external input; and outputting the NC program for finish shape image data designated by the external input to a machining tool so that the machining tool is operated based on the output NC program, wherein the generating of the image data of the machining finish shape as the finish shape image data comprises: generating a removal shape, which is a shape to be removed from the image data, based on the NC programs created in the past, and generating the finish shape image data based on the removal shape.