A tool path modification device according to an embodiment of the present disclosure, which enables high precision machining with a small computational load, is provided with: a tool path acquisition unit that acquires tool path information that specifies a tool path along which a tool for machining a workpiece travels using the coordinates of a plurality of command points through which the tool should pass; a command point adjustment unit that modifies the tool path information by changing the coordinates of the command points or adding or removing the command points; a curvilinearization section extraction unit that extracts, from the tool path information modified by the command point adjustment unit, a curvilinearization section for curvilinearizing the tool path; a tool path curvilinearization unit that replaces the information of the curvilinearization section in the tool path information modified by the command point adjustment unit with curve information; and a tool path output unit that outputs the tool path information after the tool path curvilinearization unit has replaced the information of the curvilinearization section.