An image forming apparatus has a printing section and a document reading section. The printing section prints on paper while transporting it. The document reading section includes a document transport portion which automatically transports, sheet by sheet, a document placed thereon. The document reading section generates image data by reading the document. The document reading section is operable in an ordinary reading mode in which it reads the document at a previously determined ordinary speed and in a quiet reading mode in which it reads the document at a quiet speed lower than the ordinary speed. The document reading section reads the document in the quiet reading mode when the printing section is not printing and in the ordinary reading mode when the printing section is printing.