To provide a light irradiation device capable of changing directions of irradiating light by deflecting both polarized components of incident light by using a liquid crystal cell.

The light irradiation device includes a laminated two-layer structure of a first light deflecting liquid crystal cell including a prism layer forming a long prism extending in a predetermined direction, an oriented film formed on the prism layer, and a liquid crystal layer containing liquid crystal molecules with a major axis direction oriented in a prism-length direction at an interface with the oriented film, and a second light deflecting liquid crystal cell including a prism layer forming a long prism extending in a predetermined direction, an oriented film formed on the prism layer, and a liquid crystal layer containing liquid crystal molecules with a major axis direction oriented in direction perpendicular to the prism-length direction at an interface with the oriented film. Further, the device includes a voltage applying device applying voltages to the light deflecting liquid crystal cells and an incident optical system making light incident to the light deflecting liquid crystal cells.