PURPOSE: To correct abrasion of a tool automatically by inputting a measured extension value into DNC (Group manage system) while performing add/subtract or providing preliminary code to stored an NC working information thus editing the NC working information.

CONSTITUTION: Pre-measured extension of a tool is inputted through I/O pulse 14 to central arithmetic control section 15 where with response to a required NC drive, it is added to a feed shaft or preliminary code is provided to the NC device and the result is reflected onto NC data stored in a memory 16. After completing process, DNC operating command is provided from an input machine 13 and transferred in the form of NC data to NC device side through input processing section 3. Consequently tool correction process is not required at NC device side, and an operator is not required for every NC device.