PURPOSE:To accelerate the detection of abnormality, by providing a means which transfers the abnormality when the counted output of the absolute value of a pulse encoder goes to an incorrect value, to a numerical controller (NC). CONSTITUTION:A movement detecting part 1 detects the movement of an object whose position is to be detected, and outputs a signal D having information regarding said movement. A clock synchronizing information processing part 2 inputs the above stated signal D and a clock pulse CLK from a clock generator 3, and processes the signal D, taking synchronization with the CLK. A clock abnormality detecting part 4 inputs the above stated CLK, and a part CP having the information representing at least the presence/absence of the movement of the object whose position is to be detected, out of the above stated signal D, and when the movement is detected by the above stated CP regardless of the stop of the CLK, it outputs a clock abnormality signal.
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