Technology is provided that can extract an unknown surface shape of a physical object with good precision. Image data of a proj ective image that has been acquired by radiation projection to an object is acquired. Next, a predetermined mesh structure is used to acquire cross-sectional images of the subject from image data of the projective images by reconstruction using tomography. Lattice points constituting the mesh structure are then moved in conformity with the surface shape of the object, based on the cross-sectional image that has been acquired by reconstruction. Reconstruction is carried out again using the mesh whose lattice point positions have been corrected. Movement on the reconstruction of the lattice points is then repeated as many times as required.
