A method for rewriting data in a three-dimensional optical memory element created in glass with ultrashort light pulse includes creating a bit due to a photo-induced contrast in index of refraction inside the glass in three dimensions depending of the strength of a first ultrashort-pulse laser beam. Then, irradiating the bit created in three dimensions with a second ultrashort-pulse laser beam having a lower energy than the strength of the first ultrashort-pulse laser beam while condensing the second ultrashort-pulse laser beam with an optical lens at a point shifted from the bit to be moved by a predetermined distance in an opposite direction from the direction of propagation of the first and second ultrashort pulse laser beams, thereby moving the bit for rewriting.