A method of and an apparatus for managing defective sectors in an information recording medium such as a write-once optical disk and rewritable optical disk in which many defective sectors may be generated and unevenly distributed. In the medium, primary alternative zones are formed which are composed of: a prime area for recording user data the capacity of which is variable according to the volume capacity and partition capacity and the occurrence rate of defective sectors; a primary spare area for recording alternative sectors; and a primary defect list area for recording a primary defect list. Many defective sectors are managed in the units of alternative zones. When defective sectors cannot be substituted in an alternative zone (e.g., when defective sectors are locally concentrated), defective sectors are managed hierarchically using a secondary alternative zone, thereby reducing the amount of information to be handled for the management of defective sectors. Therefore, the size of the apparatus can be reduced, and defective sectors can be rapidly searched.