PURPOSE: To eliminate the wasteful use of measurement time by decoding the contents of the working program when the working program is searched, confirming only the tool used in work, and measuring the tool length, when the tool length is measured before a workpiece is loaded.

CONSTITUTION: A file 1 of the numbers of all the set-up tools and a working program file 10 are taken into a working program searcher 2. The tool number used in work is taken into a file 3. Further, the tool length of the tool number is measured by a tool length measuring device 4. Accordingly, when the working program is searched, the working program is decoded by the working program searcher 2. Accordingly, the number of the tool which is used in the work among all the prepared tools is accommodated into the file 3. When the tool length is measured, the tool number used in the work is taken out from the file 3, and only the tool used in the work is measured all at once by the tool length measuring device 4.