A method and apparatus for relocating the data in defect sectors having occurred in the storage medium of an information recording and reproducing apparatus is described. If a defect occurs in a sector of a user area, the data of it is relocated to a temporary storage area. The logical block addresses (LBA's) for a group of sectors including an alternate sector are sequentially reassigned by skipping the defective sector and including the alternate sector. Data in the group of sectors are read out from the rear part of the user area according to current LBAs, and written according to new LBAs. Since the addresses of new LBAs are smaller than those of current LBAs by the number of defect sectors, the original data is not destroyed in the writing.