A machine which can detect flaws larger than 30μm produced by the barrel finishing process on edges of vanes is developed. The edge part is illuminated from the direction of ±60°, which is measured from the vector normal to the edge, in a plane composed of an edge and a normal vector. The flaw on the edge is detected with a lens and a CCD camera. A detectable angle of the flaw surface is analyzed theoretically and compared with experimental results. A method of classifying the detected images into two groups, the dust images and the flaw images, is also developed. When the angle between the flaw surface and one of the surfaces of the edge is small, the flaw cannot be detected. However, when the above-mentioned angle is in the region of 90± 10.6°, all flaws can be automatically detected.