ULTRAVIOLET IRRADIATION HEAD AND ULTRAVIOLET IRRADIATOR

A heat sink is thermally connected to a substrate on which LED elements are mounted. A fan unit is arranged near the distal end of a fin segment of the heat sink. A vent hole is formed in a case so as to expose the base end of the fin segment entirely in a direction in which fins are aligned. The heat sink is configured such that a gap between the fins is substantially blocked in a part except where the vent hole is present. The gap is an opening extending in a width direction perpendicular to the direction in which the fins are aligned. Space between the distal end of the fin segment and the fan unit functions as a pressure chamber that is placed in a positively pressurized condition or a negatively pressurized condition by cooling air traveling from the fan unit.