A method of erasing data of an optical disk is provided to erase data of the optical disk reliably and to prevent the danger of hacking the data stream by overwriting the null data on a data area of the optical disk. A large sized beam spot is formed over a plurality of tracks of an optical disk and the laser power value is increased when a data erasing mode of the optical disk is set. The null data is overwritten randomly on a data area of the optical disk by using the large sized beam spot while the tracking servo is off.
