The present invention relates to an apparatus for detecting defects on a disk surface which projects light on the disk surface by a light transmitting system, receives specula reflection light and scattered light by a light receiving system, exposes defects by performing a two-dimensional frequency filter process on a signal, and performs a defect determination process to extract a linear-shaped isolative defect candidate. Next, the present invention performs a periodicity determination process to classify and detect the periodically generated linear and circular arc defects and the isolatively generated linear and circular arc defects.