In a settling judgment method for judging whether an object is settled at a target position, a margin for settling judgment is expanded, and settling is judged accurately. As the settling judgment formula of the settling judgment block, both the position error and the added value of the position errors of a plurality of samples are used. Particularly for the vibration in the low frequency area, the margin for settling judgment increases. Therefore even if vibration exists in the low frequency area, judging as deviation from the settling judgment conditions by mistake can be decreased, and operations (e.g. read/write operation) can be continued.