A system for reloading pitch error correction data at the time of replacing a movable part constituting part of a mechanical system of a numerically controlled machine tool. A command to reload the pitch error correction data is preset in a machining program at the time of replacing the movable part. A numerical control device reads this command. If a parameter reload command is given (S1), and if it is the pitch error correction data (S2), it is determined whether the movable part is situated at the original position (S3), and the pitch error correction data is automatically reloaded (S4). Accordingly, the operator is not required to carry out any operation related to the reloading of the pitch error correction data, and thus the machining can be effected with the use of correct pitch error correction data.