A light irradiation apparatus, comprising: a plurality of light irradiation modules arranged; and a casing which houses at least part of the plurality of light irradiation modules, wherein the plurality of light irradiation modules each comprises a light irradiation device in which a plurality of light-emitting elements for emitting ultraviolet light are disposed on one main face thereof, a heat-dissipating member in which the light irradiation device is disposed on a first main face thereof, a cooling piping for supply which supplies a coolant to a flow channel provided inside the heat-dissipating member and a cooling piping for discharge which discharges a coolant from the flow channel, each of which is connected to a second main face of the heat-dissipating member, the second main face being located to be opposite to the first main face, an electrical wiring connected to the light irradiation device, the electrical wiring supplying power to the light irradiation device, and a cover configured to face with the second main face of the heat-dissipating member, the cover comprising through holes through which the cooling piping for supply, the cooling piping for discharge, and the electrical wiring are passed, the casing comprises a side-cover disposed along a direction from the light irradiation device toward the cover and configured to surround the plurality of light irradiation modules, and an under-cover which is connected to the side-cover, contacts with a portion of the cover of each of the plurality of light irradiation modules, and has openings through which the cooling piping for supply, the cooling piping for discharge, and the electrical wiring are passed. a plurality of light irradiation modules arranged; and a casing which houses at least part of the plurality of light irradiation modules, wherein the plurality of light irradiation modules each comprises a light irradiation device in which a plurality of light-emitting elements for emitting ultraviolet light are disposed on one main face thereof, a heat-dissipating member in which the light irradiation device is disposed on a first main face thereof, a cooling piping for supply which supplies a coolant to a flow channel provided inside the heat-dissipating member and a cooling piping for discharge which discharges a coolant from the flow channel, each of which is connected to a second main face of the heat-dissipating member, the second main face being located to be opposite to the first main face, an electrical wiring connected to the light irradiation device, the electrical wiring supplying power to the light irradiation device, and a cover configured to face with the second main face of the heat-dissipating member, the cover comprising through holes through which the cooling piping for supply, the cooling piping for discharge, and the electrical wiring are passed, a light irradiation device in which a plurality of light-emitting elements for emitting ultraviolet light are disposed on one main face thereof, a heat-dissipating member in which the light irradiation device is disposed on a first main face thereof, a cooling piping for supply which supplies a coolant to a flow channel provided inside the heat-dissipating member and a cooling piping for discharge which discharges a coolant from the flow channel, each of which is connected to a second main face of the heat-dissipating member, the second main face being located to be opposite to the first main face, an electrical wiring connected to the light irradiation device, the electrical wiring supplying power to the light irradiation device, and a cover configured to face with the second main face of the heat-dissipating member, the cover comprising through holes through which the cooling piping for supply, the cooling piping for discharge, and the electrical wiring are passed, the casing comprises a side-cover disposed along a direction from the light irradiation device toward the cover and configured to surround the plurality of light irradiation modules, and an under-cover which is connected to the side-cover, contacts with a portion of the cover of each of the plurality of light irradiation modules, and has openings through which the cooling piping for supply, the cooling piping for discharge, and the electrical wiring are passed. a side-cover disposed along a direction from the light irradiation device toward the cover and configured to surround the plurality of light irradiation modules, and an under-cover which is connected to the side-cover, contacts with a portion of the cover of each of the plurality of light irradiation modules, and has openings through which the cooling piping for supply, the cooling piping for discharge, and the electrical wiring are passed.