A tool path-generating method for computing a tool path to process a workpiece, wherein the tool path for a designated tool when processing using the designated tool is previously established. The tool path-generating method includes a path-computing process for computing, on the basis of the tool path for the designated tool, the tool path of a substitute tool differing from the designated tool when processing with the substitute tool. The path-computing process computes the portion that ultimately forms the machined surface when the workpiece is processed using the designated tool and sets the tool path for the substitute tool on the basis of the portion that ultimately forms the machined surface.