Alignment method for an image reading apparatus

An alignment method for an image reading apparatus comprising:

• a light source unit, which emits a light beam for illuminating an original placed on an original table;
• a photoelectric conversion element, in which a plurality of reading pixels are arrayed in a main scanning direction so as to convert an optical image into an electric signal;
• and
• an imaging optical system for imaging, onto the photoelectric conversion element, the light beam from the original that is illuminated by the light beam emitted from the light source unit,
• the imaging optical system comprising:
• a first optical element, which is arranged inside a first lens barrel, and has an optical surface that is rotationally symmetric about an optical axis;
• and
• a second optical element, which is arranged on an optical path between the first lens barrel and the photoelectric conversion element, and has an optical surface that is rotationally asymmetric about the optical axis,
• the alignment method comprising an alignment step of aligning at least one of an attaching angle and an attaching position of the second optical element in a sub scanning direction relative to the first lens barrel.