The invention provides a light irradiation apparatus that can adjust widening/narrowing of a light irradiation area and can guide almost whole of light emitted from an LED to the light irradiation area.The apparatus has an LED 11 and an optical unit 2 for making light for the LED 11 pass through itself and emit from its apical surface 21, and is equipped further with a supporting body 1A for holding the LED on the apical surface and a position adjustment mechanism for adjusting a relative position of the optical unit 2 to the LED 11 along an optical axis C direction. The apparatus is configured so that the potion adjustment mechanism make the optical unit 2 move relative to the LED 11 between a proximity position P1 at which a part or the whole of the supporting body 1A is housed in a base end recess 25 and a clearance position P2 at which substantially whole of the supporting body 1A comes out of the base end recess 25 so that the apical surface of the supporting body 1A and a base end face 22 of the optical unit 2 become substantially the same height.