A method of restoring phase information using a phase-contrast method, which can improve estimated accuracy of a phase. This method is a method of restoring phase information by detecting intensity of radiation, and includes the steps of: (a) obtaining three first differential signals representing differentials between one image signal and another image signal based on four image signals obtained by detecting intensity of radiation on four planes and representing radiation image information respectively; (b) obtaining second and third differential signals representing differentials between image signals relative to two directions orthogonal to each other within the planes with respect to the three image signals; (c) obtaining a Laplacian of phase based on the three image signals and three sets of the first to third differential signals; and (d) performing inverse Laplacian operation on the Laplacian of phase so as to restore phase information.