An optical element is disclosed which includes a multilayer film having a light-transmission function for light in the entire wavelength range impinging thereon at a predetermined incident angle and a polarization splitting function for S-polarized light and P-polarized light impinging thereon at another incident angle. The optical element includes two entrance surfaces, one emergence surface, three transmissive surfaces each of which faces a reflective image-forming element, and first and second optical structures respectively formed along first and second planes intersecting each other. The all normals to the above surfaces and the first and second planes are parallel to a same plane. The optical element satisfies 45°