To provide a light irradiation device capable of easily removing and reducing hair with low power light without burden on skin. The light irradiation device according to the present invention includes a light source giving pulses of light in a wavelength range from 400 to 1200 nm and a light guide distributing the pulses of light given from the light source with energy intensity of 0.2 to 10 J/cm2 at a predetermined distance from the light outgoing surface.