PURPOSE: To reduce costs, by presetting the position information of an absolute encoder for each shaft through a multiplexer to a present position register, and updating the content by the lowest bit without passing through the multiplexer.

CONSTITUTION: The outputs of absolute encoders 103XW103Z, which detect the positions of the shafts of a movable part of a machine tool, are applied to a low speed receiver 107 of an NC apparatus 101 through a multiplexer 104. The lowest bit is directly applied to a high speed receiver circuit 105 of the apparatus 101. The present position is stored in a work memory 101d in the apparatus 101. When a power source is turned ON at the operation, which is performed tomorrow, the apparatus 101 receives the detected signal and outputs an enable signal PES to the multiplexer 104. The present position memory is restored in the memory 101d. After the specified time, the multiplexer 104 stops the function, and the memory 101d is operated through the circuit 105. Therefore, an inexpensive device can be used for the receiver 107.