A light irradiation device is an apparatus for irradiating an irradiation object, and includes a light source outputting readout light L1, a spatial light modulator modulating the readout light L1 in phase to output modulated light L2, and a both-sided telecentric optical system including a first lens optically coupled to a phase modulation plane of the spatial light modulator and a second lens optically coupled between the first lens and the irradiation object, and optically coupling the phase modulation plane and the irradiation object. An optical distance between the phase modulation plane and the first lens is substantially equal to a focal length of the first lens. The spatial light modulator displays a Fresnel type kinoform on the phase modulation plane.