A tool path generating device for generating a machining program is provided with a determining unit which determines whether or not the effective cutting length of a tool would be insufficient if machining were performed using a first tool path, and an estimating unit which estimates a section of insufficiency, being the section in which the effective cutting length of the tool is insufficient. The tool path generating device is provided with a post-move travel path generating unit which generates a post-move tool path in which the path corresponding to the section of insufficiency has been moved relative to the first tool path to a path whereby the section of insufficiency can be machined using the section of the tool within the effective cutting length, and an auxiliary path generating unit which generates an auxiliary tool path for machining the uncut section remaining in the workpiece.