In this research, we studied on the influence of a flaw form, flaw size and a flaw depth to a radiographic contrast, and we sought for relation of a flaw depth and a radiographic contrast fixed quantity by calculation about flaws with various forms and sizes, and it was clarified to be able to measure a flaw height using a radiographic contrast having no relation with a flaw form, flaw size and a flaw depth by making a film-test specimen distance proper.