An optical scanning device, comprising: a light source with a plurality of emission points (31,32,33,34) for emitting beams of light; a deflector for deflecting and scanning the beams of light by reflecting the beams of light; an imaging optical system (51, 52, 53, 54, 55, 56A, 56B) for imaging the deflected and scanned beams of light on a surface to be scanned; a housing for housing at least the deflector and the imaging optical system; a synchronization sensor (6, 6A, 6B) for receiving the deflected and scanned beams of light and outputting a detection signal indicating light reception; a circuit board on which the light source and the synchronization sensor are mounted; and an adjustment mechanism for enabling an adjustment of an interval between the beams of light respectively emitted from the plurality of emission points on the surface to be scanned by rotating the light source about an optical axis of the light source; wherein: 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 light source includes a light emitter with the plurality of emission points and a lead portion for feeding power to the light emitter and the light emitter is caused to stand at a predetermined height above the circuit board by the lead portion; the adjustment mechanism includes a holding member for fixedly holding the light emitter, the holding member being fixedly mounted on an outer surface of the housing with the interval adjusted; and the circuit board is fixed to the housing in a state that the lead portion takes up the rotation of the light emitter about the optical axis by a twisting movement thereof. a light source with a plurality of emission points (31,32,33,34) for emitting beams of light; a deflector for deflecting and scanning the beams of light by reflecting the beams of light; an imaging optical system (51, 52, 53, 54, 55, 56A, 56B) for imaging the deflected and scanned beams of light on a surface to be scanned; a housing for housing at least the deflector and the imaging optical system; a synchronization sensor (6, 6A, 6B) for receiving the deflected and scanned beams of light and outputting a detection signal indicating light reception; a circuit board on which the light source and the synchronization sensor are mounted; and an adjustment mechanism for enabling an adjustment of an interval between the beams of light respectively emitted from the plurality of emission points on the surface to be scanned by rotating the light source about an optical axis of the light source; wherein: 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 light source includes a light emitter with the plurality of emission points and a lead portion for feeding power to the light emitter and the light emitter is caused to stand at a predetermined height above the circuit board by the lead portion; the adjustment mechanism includes a holding member for fixedly holding the light emitter, the holding member being fixedly mounted on an outer surface of the housing with the interval adjusted; and the circuit board is fixed to the housing in a state that the lead portion takes up the rotation of the light emitter about the optical axis by a twisting movement thereof. 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 light source includes a light emitter with the plurality of emission points and a lead portion for feeding power to the light emitter and the light emitter is caused to stand at a predetermined height above the circuit board by the lead portion; the adjustment mechanism includes a holding member for fixedly holding the light emitter, the holding member being fixedly mounted on an outer surface of the housing with the interval adjusted; and the circuit board is fixed to the housing in a state that the lead portion takes up the rotation of the light emitter about the optical axis by a twisting movement thereof.