A light irradiation device present disclosure includes at least one first light source that emits first light in a wavelength band for treating skin, an erythema detector that obtains color information of the skin to detect whether erythema of the skin is generated by irradiation of the first light, and a control unit that determines whether erythema is generated on the basis of the color information and controls driving of the first light source according to whether erythema is generated. The erythema detector includes at least one second light source that emits second light in a visible light wavelength band to the skin, and at least one sensor that receives the second light traveling through the skin.