An optical illumination system wherein an increased amount of light from a light source can reach a light valve, in which a luminous flux of the light source is irradiated upon a first lens array. The luminous flux having passed through the first lens array is introduced to the polarization conversion system provided immediately before a second lens array, and a luminous flux coming out from the polarization conversion system is introduced to the second lens array and then irradiated upon the light valve. The first lens array has an image forming position f which satisfies S