An optical scanning device includes a light source, a deflector for deflecting and scanning the beams of light, an imaging optical system, a housing, a synchronization sensor, a circuit board on which the light source and the synchronization sensor are mounted, and an adjustment mechanism. The adjustment mechanism enables an adjustment of an interval between beams of light respectively emitted from the plurality of emission points on a surface to be scanned. The circuit board includes a first part on which the light source is mounted, a second part on which the synchronization sensor is mounted and an intermediate part between the first and second parts. The first part is arranged outside the housing, the second part is arranged inside the housing and the intermediate part passes through a wall surface of the housing. The adjustment mechanism fixes the light source using the housing with the interval adjusted.