Light irradiation device and light irradiation method

The invention provides a light irradiation device and a light irradiation method which last an effect of removing an organic matter to be the same as the present, and avoid an occurrence of defectives etc. resulting from static electricity caused by a photoelectric effect even in the case of irradiating a light on an irradiated matter that contains a metal wire or produces a photoelectric effect. The light irradiation device is a UV irradiation device applied to irradiate UV on an irradiated matter and remove the organic matter adhering to the irradiated matter, and including a light source emitting a light containing a UV shorter than a specific wave length, and a metal reflective mirror reflecting the light emitted from the light source to a side where the irradiated matter is, a separation distance between the reflective mirror and the irradiated matter being set to be shorter than a distance of possible existence of an electron flying from a reflective face of the reflective mirror using UV.