A moved distance detecting means detects the moved distance in a tracking direction of an object lens, a position signal generating means generates a position signal corresponding to the position of the object lens based on the detection, and a drive signal modulating means modulates the drive current of a magnetic head according to this position signal. In some embodiments, a testing framework generates a set of test cases for a system under test using a grammar. The locking device also includes a compression device mounted so that it sides in the sleeve and is capable of increasing a contact pressure between the indexing means after screwing. In addition, the device can be converted for either right hand use or left hand use.