A quantum cascade laser manufacturing method includes: a step of pressing a mother stamper against a resin film having flexibility to make a resin stamper 201 having a second groove pattern P2; a step of making a wafer with an active layer formed on a semiconductor substrate; a step of forming a resist film 304 on a surface on the active layer side of the wafer; a step of pressing the resin stamper against the resist film 304 by air pressure to form a third groove pattern P3 on the resist film 304; and a step of etching the wafer with the resist film 304 serving as a mask to form a diffraction grating on a surface of the wafer.