The present invention is to allow for an automatic correction of an offset amount of a tool used in actual workpiece processing at an appropriate timing. The present invention provides a numerical control device for a machine tool including: an execution unit for executing a processing program; a storage unit for storing, for each tool used in each processing program, a wear amount of the each tool when executing the processing program, as a tool offset amount; a monitoring unit for monitoring the timing of the work processing end or work processing start; and a changing unit for changing, for each processing program, the present tool offset amount at the timing of the work processing end or work processing start monitored by the monitoring unit, on the basis of the tool offset amount of the processing program stored in the storage unit.