In a numerical control of a machine tool, the relation between the total number of instructions, or the range of movement of the movable member of the machine tool and the actual amount of movement is not represented by a straight line but periodically change sinusoidally over substantially equal ranges of movement, due to a lead error of a ball screw used for moving the movable element. For the purpose of correctly compensate the position error in a short time, the total range of movement of the movable element is divided into a plurality of ranges, and start and end points of movement, types of movement of respective ranges and periods thereof are stored in memory means. The actual position of the movable element and the data stored in the memory means are used to correct the actual position of the movable member.