Disclosed data recording techniques prevent extremely decreasing writing/reading speed due to consecutive defects, which often occur when using a disk of large storage capacity, while allowing the size of a spare area used for alternate processing of a recordable optical disk to be changed. The disclosed data recording method comprises receiving from a higher-level device a write command to write data at a first address in a user area; writing the data at the first address; and reading the written data to thereby judge whether or not the first address is defective. If the first address is defective, a second address in a spare area is determined by use of a flag value that has been written to a lead-in area or a lead-out area at the time of initialization; and the data is written at the second address received from the higher-level device.