The present invention accurately predicts postoperative intraocular lens position on the basis of a shape image of the crystalline lens obtained by an optical interference tomographic imaging device. This makes it possible to reduce the postoperative refractive error and determine the power of the intraocular lens. The present invention comprises: a step for finding by computer the equatorial position, which is the site of maximum diameter in the crystalline lens, from the morphology of the crystalline lens obtained from a tomographic image of the patients eye generated by the optical interference tomographic imaging device; and a step for estimating the position of the intraocular lens from the equatorial position thus found.