SCANNING OPTICAL DEVICE

A scanning optical system receives a light beam deflected by an optical deflector and forms an image on an image surface. A window member transmits the light beam deflected by the optical deflector. An optical sensor detects the light beam that passes through the window member. A frame has a mount surface on which the optical deflector is mounted. The frame includes a first wall having a first opening and a second opening. The light beam directed from the optical deflector toward the scanning optical system passes through the first opening. The light beam directed from the optical deflector toward the optical sensor passes through the second opening. The first opening is closed by a closest scanning lens to the optical deflector in the scanning optical system. The second opening is closed by the window member.