Image forming apparatus and image forming method

An image forming apparatus comprising:

• a document reader that reads a plurality of documents having different sizes in a main scanning direction;
• a document size detector that detects a main scanning direction size and a sub-scanning direction size of each document;
• an image processor that performs image processing on an image of the read document;
• a printer that prints, on a printing sheet of a fixed size, the image that has or has not undergone the image processing;
• one or more post-processors that perform post-processing on a plurality of printing sheets having a same main scanning direction size according to a user setting;
• and
• one or more controllers that control reading of the document, the image processing, the printing, and the post-processing, wherein
• in a case where the post-processing is set, and when the main scanning direction size is alignable to a main scanning direction size of one of the documents by applying, to an image of each document, at least one of image processing among rotation in the unit of 90 degrees, enlargement/reduction, and margin increase/decrease adjustment, the one or more controllers allow to perform the post-processing by aligning the main scanning direction size of each image with respect to the alignable size as a reference size.