To realize an image forming device which efficiently executes the reading of a both-side original and the both-side printing of a recording sheet.

In the case of executing the both-side printing of the image data of an original printed on both sides on the recording sheet with the printing means of a printer 100, the first surface of the recording sheet is printed by the image data read by an image reading head 202, and the second surface of the recording sheet is printed by the image data stored by a page memory 110. Thus, the second surface of the original is read and is stored in the page memory even during the printing of the first surface of the recording sheet, so that both-side printing of the original recorded on both sides is efficiently executed.