A scanning optical apparatus includes a deflection element configured to deflect a laser beam emitted from a light source for scanning, a mirror member configured to directly reflect the laser beam deflected by the deflection element toward a surface to be scanned, and an optical box configured to house the deflection element and the mirror member. The optical box includes a bottom plate portion and a sidewall portion that encloses the bottom plate portion. The scanning optical apparatus further includes a plate-shaped connection portion configured to connect an opening surface of the optical box that faces the bottom plate portion from one side to the other side of the sidewall portion. The connection portion is provided at a position where it does not overlap with the mirror member in a direction orthogonal to the bottom plate portion.