PURPOSE: To provide an NC data editing device capable of automatically editing a plurality of NC data to one by a simple operation even when an operator is not so knowledgeable about NC data making, its operation and its editing operation in a case where a plurality of NC data are edited as one.

CONSTITUTION: An NC data editing method is for editing a plurality of NC data made to process one or more articles to be processed to one in order to perform processing on the same machine tool. This method comprises a step (S5) for sequentially extracting tool number command data from the lead program of the NC data with respect to each NC data from the plurality of NC data, a step (S6) for comparing the tool number command data thereof and lumping the same tool number having similar processing steps together to one and editing process steps (S8 and S9) for rearraying the NC data for each tool number command data in order of the lumped together tool number command data.