The present invention provides a polarized light irradiation device capable of setting an alignment azimuth angle θ of liquid crystal molecules to be a desired angle even when the incident angle of polarized light on a substrate is not 0° in irradiation of a photo alignment film with polarized light, and a method for manufacturing a liquid crystal display device by using the polarized light irradiation device. The polarized light irradiation device is used in alignment treatment of a photo alignment film provided on a substrate, the device including: a stage including a placement surface on which the substrate is placed; and a polarized light irradiation unit configured to irradiate the placement surface with polarized light through a polarizer in a direction tilted relative to the normal of the placement surface, wherein a polarization azimuth angle α, which is an angle of the polarization axis of the polarizer when the polarization axis of the polarizer is projected onto the placement surface, satisfies 30°