A read-only recording medium and a reproducing method thereof ensures reproduction compatibility with a rewritable recording medium in which real data is recorded with substantial discontinuity. The read-only recording medium comprises a data recording area in which real data is stored; and a plurality of waste areas allocated at intervals in the data recording area. The method of reproducing data stored in a read-only recording medium reproduces data from the read-only recording medium, skips if a waste area is encountered or removes invalid data reproduced from the waste area wherein each waste area has been inserted periodically in the read-only recording medium, and outputs the data reproduced before and behind each waste area in succession. As a result, the playability is improved in a disk device capable of reproducing both a read-only and a rewritable recording medium.