An optical system for image projection is disclosed which is capable of improving contrast while suppressing reduction of light amount. The optical system includes a converging optical system, and a polarization beam splitting surface transmitting an incoming light flux having a first polarization direction from the converging optical system, to introduce it to the image-forming element and causing light having a second polarization direction, of an outgoing light flux from the image-forming element, to proceed to a projection optical system. In a first cross-section parallel to a normal to the polarization beam splitting surface, the converging optical system has a configuration causing an incident angle on the splitting surface of a light ray passing through a barycenter of intensity distribution of the outgoing light flux to be larger than an incident angle thereon of a light ray passing through a barycenter of intensity distribution of the incoming light flux.