There is provided a light irradiation device capable of adjusting enlargement/reduction of a light irradiation area and introducing almost all the light emitted from an LED element without loss to the light irradiation area. The light irradiation device includes an LED element (11) and an optical unit (2) passing the light from the LED element (11) and emitting it from an end surface (21). The light irradiation device further includes an element holding body (1A) for holding the LED element (11) at the end surface, and a position adjusting mechanism for adjusting the relative position of the optical unit (2) with respect to the LED element (11) along an optical axis C. The position adjusting mechanism relatively moves the optical unit (2) with respect to the LED element (11) between an approximate position (P1) where the element holding body (1A) is partially or entirely contained in a base indentation (25) and an apart position (P2) where the element holding body (1A) is substantially entirely out of the base indentation (25) and the end surface of the element holding body (1A) is substantially at the same height as the base surface (22) of the optical unit (2).
