A data erasing method of the present disclosure is a data erasing method for erasing data stripe-recorded in a plurality of write-once optical discs constituting a redundant arrays of inexpensive disks (RAID) system and each including a plurality of data recording blocks and a redundant data block. In the data erasing method, alternate recording of at least one target block and the redundant data block is performed in a predetermined alternate area. The target block is one of the data recording blocks in which target data as erase target data is recorded. The target block is overwritten such that the target data is not correctly read.