When creating other tool path from two tool paths for cutting a work accurately and efficiently, the data on the first tool path (11) is composed of a position vector (14) and a direction vector (15) of a tool for use when the work is cut while moving the tool. The data on the second tool path (21) is composed of a position vector (24) and a direction vector (25) of the tool for use when the work, which has been cut according to the first tool path, is further cut. A computer (50) uses the first tool path (11) data and second tool path (21) data to calculate a position vector (64) and a direction vector (65) of a medium tool path (61) that is between the first tool path (11) and second tool path (21). <IMAGE>
