A method for writing a signal on an optical disk is disclosed. The optical disk comprises a track groove on a recording surface thereof, on which information is recorded along the track groove on a block-by-block basis each said block having a predetermined length and where an identification mark indicating the beginning of each said block, has been formed on the track groove. Writing is started before the identification mark, located at the beginning of at least one block on which the signal should be written, is reached and writing is ended after the identification mark located at the end of the at least one block on which the signal should be written has been passed.