To make old holograms easy to read by successively reading out an oldest good page and making it a next self-erasing page, rewriting data in a free page, then, making it a newest good page and making the oldest self-erasing page a free page to reduce a change in a refractive index.

P pieces of pages are arranged in slots in circular order. Memory pages are arranged in slots in the circular order and are classified into good pages (g), secularly self-erasing pages (s) or a free page (e) which are regarded as to be writable. Then, 0.36×P pieces of pages in the slots form the low-order segments of a circle and are arranged in the clockwise direction in the order of elapsed times. A good page being at the most leading end in the clockwise direction is read out and rewriting is performed at one point in the counterclockwise direction and refreshing operations of all good pages are completed by successively performing this operation. Thus, low-order segments of the good pages are moved respectively by one slot as of the respective refreshing operations.