Abstract: A laser processing device and a laser processing method that are capable of forming a high-quality semiconductor film are provided. An ELA device (excimer laser annealing device) (1) includes a laser oscillator (10) that generates laser light for forming a polysilicon film by irradiating an amorphous silicon film over a substrate to be processed with the laser light, a pulse measuring instrument (100) for detecting first partial light and second partial light contained in the laser light, and a monitoring device (60) for comparing a detection result of the first partial light with a detection result of the second partial light.