Band-narrowing module, band-narrowing laser device, and method for positioning band-narrowing module

This band-narrowing module may comprise: a grating device including a grating that narrows the band of a laser beam, and a holder that holds the grating; a housing that houses the grating device; and a grating moving device that supports the barycentric position of the grating device, or a position in the vicinity thereof, from a direction substantially perpendicular to the dispersion plane of the grating, and that moves the grating device with respect to the housing in the direction substantially perpendicular to the dispersion plane of the grating.