The invention provides an optical scanner and an image forming apparatus with a loopback mirror being positioned with high accuracy, the deterioration of an image due to the vibration of an optical box is prevented, and assembly is simplified at low cost, even when the loopback mirror is arranged directed outward with respect to the optical box. The optical scanner has a light source; a light deflector for scanning the light beam emitted from the light source; and a single or a plurality of loopback mirrors for exposing/scanning a face to be scanned with the light beam which is deflected and scanned with the light deflector. In the optical scanner, the light source, the light deflector and the loopback mirrors are mounted in an optical box, and at least one of loopback mirrors is so arranged that the turning back mirror face side is directed to the outside of the optical box, and is positioned and fixed in the optical box. In the optical scanner, a projected part (201) formed into an arch is provided at the fixing part of the loopback mirrors in the optical box. |