A disk apparatus includes a DSP core. If given an instruction to skip music during reproducing with an MO disk, the DSP core sets to a counter a count value corresponding to the number of tracks to jump over. Then, tracking servo is turned off and an optical pickup is moved in a radial direction of the MO disk. The DSP core detects rising and trailing edges in a TZC signal and counts down the counter. When the count value becomes 1, a level of the TZC signal is determined to judge whether there is variation in offset value or not. If there is variation in offset value, edges are considered counted incorrect. Accordingly, the count value is incremented. Thus, jump can be made to a desired land or groove, i.e. access can be made positively to a target position.