In reading an image of a document in a monochromatic document reading mode, a document reading apparatus reads the image of the document while conveying the document at a speed determined according to a variable magnification ratio, executes digital variable magnification on the read multivalued image in a main scanning direction by using a main scanning direction variable magnification unit, binarizes the multivalued image, and stores the binary image on a memory. In reading an image in a color document reading mode, the document reading apparatus reads the image of the document while conveying the document at a predetermined speed, stores the read multivalued image on the memory, and executes digital variable magnification on the multivalued image in the main scanning direction and a sub scanning direction.