To provide a light irradiation device and a printing device with less thermal influence by ultraviolet irradiation.

The light irradiation device for irradiating light to an object with light transmitting property to which ultraviolet curable ink or ultraviolet curable resin is attached has a pair of light irradiating devices arranged so as to face each other in a surface to be attached of the ultraviolet curable ink or the ultraviolet curable resin of the object and a surface not to be attached located in a position opposite side to the surface to be attached respectively, the pair of light irradiating devices has a plurality of light emitting elements arranged in longitudinal and lateral lines in the base body and the main surface of the objective side of the base body, the number of the light emitting elements in the light irradiating device of the side of the surface not to be attached is less than the number of the light emitting elements in the light irradiation device of the side of the surface to be attached, thereby the thermal influence from the light emitting devices can be relatively reduced because light brightness of the light emitting elements can be relatively lowered.