A temperature sensor (131) detects a temperature of a spindle motor (121) of a rotary drive unit (120) for rotating a disk-shaped recording medium (1), and a temperature information acquiring unit (134A) acquires the temperatures as temperature information. An eccentricity detector (132) detects a drive voltage level, and an eccentricity information acquiring unit (134B) acquires the drive voltage level as eccentricity information. When a determining unit (134C) determines that the temperature is higher than a predetermined temperature or that the drive voltage level is higher than a predetermined voltage, a servo controller (133) switches a rotation mode from constant liner velocity to constant angular velocity. That enables stable information processing over a long time with a simple strucure for constant linear velocity.