Method of assembling and adjusting a multi-beam scanning optical apparatus and method of manufacturing a multi-beam scanning optical apparatus

A method of manufacturing a multi-beam scanning optical apparatus including a light source unit having multiple light emitting points, a deflecting unit configured to deflect multiple light beams emitted from the light source unit, and an imaging optical system having a first imaging optical element and configured to focus the multiple light beams deflected by the deflecting unit on a single surface to be scanned, the method comprising:

• adjusting incident positions of the multiple light beams on the first imaging optical element in a sub-scanning direction;
• and
• adjusting irradiated positions of the multiple light beams on the single surface to be scanned in the sub-scanning direction without changing the incident positions on the first imaging optical element, wherein:
• the adjusting of the incident positions and the adjusting of the irradiated positions are performed while detecting the multiple light beams with first optical sensors respectively arranged on at least two image height positions at positions corresponding to the single surface to be scanned;
• the adjusting of the incident positions is performed while detecting the multiple light beams with a second optical sensor arranged on the deflecting unit side of the first imaging optical element;
• and
• the adjusting of the irradiated positions is performed while detecting the multiple light beams with the first optical sensors.