A puncture forming method is a method of forming punctures in a sample by irradiating a surface of the sample with a light beam. The puncture forming method includes: forming a first puncture by irradiating a first position on the surface of the sample with a first pulse of the light beam; and after the forming of the first puncture, forming a second puncture which at least partially overlaps the first puncture by irradiating, with a second pulse of the light beam, a second position on the surface of the sample positioned away from the first position in a first direction. The second puncture has a tip which is positioned inside the sample and which is bent in a direction opposite to the first direction.