A light irradiation device according to an embodiment includes an excimer lamp including a light emitting tube emitting light, a first electrode disposed at an outer side of the light emitting tube, a second electrode disposed at an outer side of the light emitting tube in correspondence to the first electrode, and an auxiliary light emitting body disposed between the first electrode and the second electrode to emit light toward the light emitting tube when a voltage is applied to the first and second electrodes, and a case in which the excimer is provided and which has a contact point adjustment part configured to accommodate a portion of the auxiliary light emitting body.