1. An apparatus for processing a radiation image of an object obtained by radiography using a grid which is used to remove scattered radiation from the object, to remove image components due to the grid, comprising: generation means for generating the image components due to the grid on the basis of data of the radiation image, comprising analysis means for analyzing the radiation image to obtain a spatial frequency and optionally an angle of a periodic pattern that the image components form, extraction means for extracting predetermined components containing the image components from the radiation image on the basis of an analysis result from said analysis means, and processing means for processing the predetermined components obtained by said extraction means to obtain the image components; and removing means for removing the image components obtained by said processing means from the radiation image, wherein said processing means executes a process for estimating and processing an unsteady portion of the predetermined components from steady portions before and after the unsteady portion as the process of the predetermined components, and wherein said processing means estimates an amplitude and phase of a sine wave corresponding to the image components on the basis of the steady portions of the predetermined components before and after the unsteady portion, and the spatial frequency, and mends the unsteady portion on the basis of the estimation result.