Disclosed is a spindle control system of a numerical control apparatus capable of independently controlling a plurality of spindles by a plurality of paths. Connecting relationships between respective paths (11 to 14) and respective spindles (61 to 65) are defined in a region (3), the content of the region (3) is changed by a machining program to change the spindles (61 to 65) to be controlled by the respective paths (11 to 14), whereby a more effectively machining can be realized.