Abstract: It is determined, according to a radial position of a pickup along a radius of a disk, whether or not to cause the pickup to jump to a different track so as to reduce a time required for reaching a target position on the disk. A reference value is used for the above-mentioned determination. The determination causes the pickup to jump to the different track when the target position on the disk is located behind the pickup, and also causes the pickup to jump to the different track when the target position on the disk is in front of the pickup and a distance to the target position is larger than the reference value. The reference value is determined to correspond to approximately one turn of the track at which the pickup is currently present. A buffer memory temporarily stores data which has been read out through said reading means. In response to an externally given first data transfer request, first requested data is read out from the buffer memory if it is present therein.