A laser processing method includes a first step of emitting measurement laser light of a first wavelength from the reference surface side to a reference object having a reference surface of which reflectance for the first wavelength is known to obtain a reference light amount as a reflected light amount of the measurement laser light on the reference surface, a second step of emitting the measurement laser light from the first surface side to the object to be processed to obtain a first light amount as a reflected light amount of the measurement laser light on the first surface, and a third step of, after the first step and the second step, calculating a reflectance of the first surface for the first wavelength based on a reflectance of the reference object, the reference light amount, and the first light amount.