A default gain table stores values of loop gain of a spindle motor control unit predetermined for each number of media. A loop gain setting unit detects the number of media, reads out a loop gain corresponding to the detected number of media from the default gain table and sets it in the spindle motor control unit. A loop gain measuring unit measures the loop gain of the spindle motor control unit during a test in the manufacturing process, adjusts it into an optimum loop gain, and stores it as a default lop gain in the apparatus.