PURPOSE: To prevent damage of tool by selecting random check points on the tool moving path based on NC data and comparing their co-ordinates with the work shape data or the zig data.

CONSTITUTION: Interference decision means 4 will compare the co-ordinates at the intermediate point set on a tool moving path while fed from a register 3 with the referential data from an interference decision data memory 2 thus to decide the existence of interference. Work interference decision circuit 41 and zig interference decision circuit 42 are provided with the co-ordinates from the register 3 and upon decision of the existence of interference, route decision means 5 will retrieve a plurality of other routes to decide the optimal moving route having no interference through decision circuit. Consequently, the tool will prevent damage of zig to shorten the idle time resulting in the improvement of safety and productionability.