To provide a scanning optical apparatus which is made compact and allows a scanning lens to keep high optical performance, by suppressing the thermal influence given to the scanning lens to a low level by an air flow.

The scanning optical apparatus exposes and scans an image carrier by allowing a light beam emitted from a light source incident on a polygon mirror 3, the light beam reflected on the polygon mirror 3 reflected on a turning back mirror via f lenses (scanning lenses) 9 and 10 and focused on the image carrier, wherein the f lens 9 is fixed on a body 2 that applyies spring pressure of a spring plate metal 14, and at the same time, the f lens 9 is covered by the spring plate metal 14. A slit 14a is formed at a part of the spring plate metal 14, through which the light beam passes, and the overall part of the f lens 9 except the slit 14a of the spring plate metal 14 is covered. Furthermore, a pressurizing part 14b of the spring plate metal 14 against the f lens 9 is made into a hemispherical shape and makes the pressurizing part 14b point-contact with the f lens 9.