GROOVE PROCESSING DEVICE AND GROOVE PROCESSING METHOD

A groove processing device (100) that forms a groove in a surface of an object using laser beams (LB) includes: a light source device (11) that outputs the laser beams (LB); a polygon mirror (10) that reflects the laser beams output from the light source device (11); a condensing optical system that is provided on an optical path of the laser beams (LB) reflected by the polygon mirror (11) and focuses the laser beams (LB); and a shielding plate (35) that is provided between the condensing optical system and the object at a position which blocks some of the laser beams (LB) focused through the condensing optical system and blocks some of the laser beams (LB). Among the laser beams (LB) focused through the condensing optical system, some of the laser beams (LB) that are not blocked by the shielding plate (35) form the groove in the surface of the object at a focus of the laser beams (LB). The shielding plate (35) is provided closer to the condensing optical system than the focus and is rotated with respect to the surface of the object so as to block the laser beams (LB) that do not form the groove.