Abstract: The present invention provides a method for determining what group a given multilayer optical disc belongs to. The disc is one of a number of multilayer optical discs, which are designed so that information stored is retrievable from any of the discs by irradiating the disc with a light beam having the same wavelength and which have been classified into multiple groups. According to this method, performed first is Step (A) of measuring either a distance from a first one of multiple information layers of the given multilayer optical disc to a second one thereof, which is located adjacent to the first information layer, or a distance from the first information layer to the surface of the optical disc. Next, Step (B) of determining, by the distance measured, what group the given multilayer optical disc belongs to is performed.