Abstract: A feedrate and travelling distance before the feed orientation of a feed drive axis is obtained by analyzing NC programs when carrying out a machining action, and the lost motion correcting quantity corresponding to said feedrate and travelling distance is calculated by using the relationship obtained in advance by experiments. Furthermore, the lost motion correcting quantity obtained by calculations is overlapped onto the instruction value to a servo motor which drives the feed drive axis, when the feed orientation of said feed drive axis is reversed.