DISCRIMINATING METHOD FOR DISK WITH DIFFERENT THICKNESS AND OPTICAL PICKUP DEVICE USING SUCH METHOD

PROBLEM TO BE SOLVED: To quickly read a kind of disk and to generate a stable reproducing signal. SOLUTION: For a prescribed number of times, a focus voltage is increased/ decreased which is applied to the actuator 20 of an objective lens 21 oppositely facing a disk 30 having an information face, so that an objective lens 21 standing by at a neutral position is moved to a focus position corresponding to the disk 30. Then, when the objective lens 21 is moved to the focus position, its moving distance value is detected from the focus signal applied to the actuator 20. Subsequently, if this moving distance value is larger than the reference value, the disk is judged as a thick disk. Conversely, if the value is smaller, it is judged as a thin disk. As a result, the kind of disk 30 is quickly read, enabling a stable reproducing signal to be generated.