Abstract: A portable light irradiation device for providing a stimulus of light to the eyes of user is used to regulate biological rhythm and improve awakening level of the user. This device includes an elongate illumination unit for irradiating the light to the user's eyes, a pair of pads adapted to be fitted to sides of the user's head, a headband adapted to be fitted to a top of the user's head and coupled to the pads at opposite ends thereof, and a supporting arm extending from at least one of the pads for supporting the illumination unit at the forward end thereof such that the illumination unit can be disposed in front of the eyes of the user wearing the light irradiation device. The supporting arm is slidably supported to the pad at the rear end thereof such that a projection length of the supporting arm against the pad is adjustable.