The present invention relates to a locking device for a wire line core drilling system comprising an inner tube by means of which core samples are collected, and an outer tube connected to a drill bit, which locking device is applied in the rear end of the inner tube. Since a logic power supply voltage reduces by the same amount as the reference potential, the logic power supply voltage from a viewpoint of the reference potential is fixed. The modulation circuit outputs a modulated signal, a voltage amplitude of which varies in one pulse signal, on the basis of the corrected image data. The computer will perform preprogrammed designated audio or visual or other electronic responses to identified points on the surface by matching the identified point on the surface with an electronic version of the surface in memory and a preprogrammed task for such a match. The circuit controls an on period of the synchronous rectification switch element so as to turn on the synchronous rectification switch element in synchronization with a particular timing, and turn off in synchronization with another timing.