To provide a light irradiation device which can form a pattern faithful to a pattern of a mask and with high resolution.

The light irradiation device includes a light emission part equipped with a light source element row having a plurality of light source elements arranged in one direction, each consisting of a short-arc type discharge lamp and a reflector arranged to surround the discharge lamp for reflecting light from the discharge lamp to a parallel direction to its light axis, and a mask made by arranging a number of linear shielding parts and translucent parts extended in a perpendicular direction to the above direction arranged alternately in one direction. A plurality of shielding plates each having a light-absorbing property are arrayed in the direction in a posture extending perpendicularly to the direction along the light axis of the reflector.