PURPOSE: To make it possible to adaptively control the machining of a work piece, even if it is a complex shaped mold, by measuring the surface coordinate of the work piece beforehand, calculating a cutting cross section and the feed rate that the load acting on a tool becomes set value thereat, and commanding a feed controller based on the result of calculation.

CONSTITUTION: The contour of a work piece is measured by means of a three dimensional measuring instrument 21, and the shape is memorized in a memory 22. A cutting cross section is calculated by a calculator 24 by use of the contour data and the cutting data contour(program path). The calculated cutting cross section is input in a feed rate calculator 26 to determine the feed rate that the load acting on a tool becomes the value set by a load setting apparatus 25 thereat. The value of the feed rate is sent to a feed rate controller 13, and a work piece of a complex shape such as a mold is continuously cut always based on the value set by the load setting apparatus 25.