A tool path generation method for calculating a tool path for machining a workpiece while moving a tool relative to the workpiece, wherein a tool path of a specified tool, when the specified tool, which is a ball end mill, is used in machining, is set in advance, the tool path generation method comprising a tool path calculation step for calculating a tool path of a substitute tool, which is a ball end mill and has a tool diameter smaller than the specified tool, based on the tool path of the specified tool, when the substitute tool which is different from the specified tool performs machining, and the tool path calculation step includes: a step for calculating a portion which finally generates a machining surface in a machining area of the specified tool, when the specified tool machines the workpiece, a step for setting a range in which the substitute tool is disposed based on the portion which finally generates the machining surface, a step for setting a plurality of positions on which the substitute tool is disposed within the range in which the substitute tool is disposed, and a step for setting the tool path of the substitute tool based on the plurality of positions on which the substitute tool is disposed, the portion which finally generates the machining surface being a plane portion, characterized in that the step for setting a plurality of positions includes a step for setting a plurality of first points (p) and a plurality of second points (x) in the range in which the substitute tool is disposed, selecting one of the first points (p) nearest to each second point (x), calculating an angle (θx) between a line connecting the specified tool center and the first point (p) and a line connecting the specified tool center and the second point (x) with respect to all second points (x), increasing the number of first points (p) until a maximum angle (θxmax) is equal to or less than an angle judgment value, and setting the first points (p) as the positions on which the substitute tool is disposed. a step for calculating a portion which finally generates a machining surface in a machining area of the specified tool, when the specified tool machines the workpiece, a step for setting a range in which the substitute tool is disposed based on the portion which finally generates the machining surface, a step for setting a plurality of positions on which the substitute tool is disposed within the range in which the substitute tool is disposed, and a step for setting the tool path of the substitute tool based on the plurality of positions on which the substitute tool is disposed, the portion which finally generates the machining surface being a plane portion, characterized in that the step for setting a plurality of positions includes a step for setting a plurality of first points (p) and a plurality of second points (x) in the range in which the substitute tool is disposed, selecting one of the first points (p) nearest to each second point (x), calculating an angle (θx) between a line connecting the specified tool center and the first point (p) and a line connecting the specified tool center and the second point (x) with respect to all second points (x), increasing the number of first points (p) until a maximum angle (θxmax) is equal to or less than an angle judgment value, and setting the first points (p) as the positions on which the substitute tool is disposed.