A disk apparatus (10) includes an optical lens (14). A seek operation is performed by moving the optical lens in a radius direction of a recording surface of a magnetooptical disk (40). When the seek operation is being operated, a TE signal detection circuit (26) generates a TE signal based on a laser beam reflected from the recording surface, and applies a generated TE signal to a DSP (34) via an A/D converter (32a). The DSP detects a peak level of the TE signal and a level change amount of the TE signal in a unit time, and generates a tracking actuator control voltage based on the detected peak level and the level change amount. A moving speed of the optical lens is controlled by a generated tracking actuator control voltage.