The light irradiation device is provided that can reduce moire interference with a simple and low-cost arrangement without sacrificing a compact design by comprising a transparent plate 31 which has a predetermined thickness and one of whose surfaces is arranged as an object facing surface 31a to face an object W such as a product on which light is to be irradiated, multiple reflecting sections 32 that are laid out on other surface of the transparent plate 31 with forming a microscopic space S therebetween with its light reflecting surface facing a direction of the object W, a light source section 5 arranged at a position where at least a part of the emitted light is transmitted, reaches the light reflecting surface, is reflected on the light reflecting surface and is emitted from the object facing surface 31a, and an antireflection film 33 that covers the object facing surface 31a.