A method of determining whether a defect exists on an information storage medium is provided along with a recording/reproducing apparatus using the same. Such a method comprises: seeking a defect entry whose state information indicates that a defect block or a replacement block has been re-initialized without certification from a defect list for managing an information storage medium and including state information of the defect block and state information of the replacement block, wherein the medium includes a spare area for recording the replacement block to replace the defect block occurring in a user data area on the medium; and certifying the defect block or the replacement block registered in the sought defect entry. As a result, defect information can be effectively rearranged for quick re-initialization without certification in order to improve the performance of a drive system.