A method including a bend angle calculation step of calculating a bend angle θ at each connecting point of a broken line which is obtained by successively connecting a predetermined plurality of machining points P1 to P3 by line segments, an approximation curve derivation step of deriving an approximation curve L5 closer to the connecting point the larger the bend angle θ calculated by the bend angle calculation step, and a tool path generation step of generating a tool path PA7 along the approximation curve L5 derived by the approximation curve derivation step.