To determine whether defects such as finger prints, scratches and dust or the like, which are inadvertently put on the surface of an optical disk during recording of optical information onto the optical disk, cause recording error of the optical information within a 1RUB or not.

During the recording of the optical information onto the optical disk, defect signals are detected by utilizing a level change in the recording light beams being reflected by the recording surface of the optical disk caused by the defects on the disk surface. The time in which the level of defect signals is made equal to or less than a reference potential is taken out as a defect detection time by comparing the defect signals and the reference potential. Then, it is determined whether the defects on the optical disk cause recording error or not from the defect detection time.