There is disclosed a light projection optical system comprising a light source; a relay lens unit which has a negative lateral magnification and which converts a luminous flux that has diverged from the light source into converged light; and a projection lens unit which reduces a divergent angle of the luminous flux from the relay lens unit to convert a state of the luminous flux into a state close to that of a parallel luminous flux and which projects light toward a target region, wherein the following conditions are satisfied: 0.9