The purpose of this study is to establish an evaluation method for ballast grains shape, which effect the deformation property of ballast. In this study, the "normal argument function" and "radius functions" are calculated from the contour data of ballast grain read by a digital camera. According to the result of these analysis, it is assumed that the "flatness" or the "elongation" is decided by the value of the 2nd magnitude spectrum of "Radius function" wave of grain shape.