[Problem] Provided is a light irradiation device capable of irradiating the entire outer circumference surface of an irradiation target such as an optical fiber with light providing a high irradiation intensity while being small in size.[Solution] A light irradiation device which irradiates an irradiation target capable of relatively moving along a first direction with light includes a light source having a plurality of solid-state elements which are disposed on a substrate to be defined by the first direction and a second direction in a plurality of rows and irradiate the irradiation target with light from a third direction, an optical element which refracts light from each of the solid-state elements at a predetermined angle and emits the light as well as narrows a spread angle of light to be emitted from each of the solid-state elements with respect to the third direction, a first reflection portion which has at least two first reflection surfaces disposed on a downstream side in the third direction of the irradiation target and reflects a part of light incident on the first reflection surface from the optical element to the irradiation target, and a second reflection portion which has a pair of second reflection surfaces disposed between the optical element and the first reflection portion and guides light from the optical element to the first reflection surface.
