To provide an image forming apparatus that makes it possible to perform a both-sided printing process more easily and eliminates the need for a both-sided printing mechanism.

The both-sided printing process is performed such that paper supplied from a supply position (paper cassette or a manual insertion tray), subjected to image recording on its first side, and ejected to an ejecting position (first ejection tray or second ejection try) is resupplied from the supply position to be subjected image recording on its second side. In the both-sided printing process, only when the manual insertion tray is selected as the supply position where paper is set for recording an image on the second side (YES in step P2), the setting of the supply position is made effective (step P3). The operation of printing on the second side is started after the paper is set in the manual insertion tray which is exposed outside to allow easy setting of the paper, unlike the paper cassette that needs to be pulled out of the image forming apparatus in order to set paper. Thus, the both-sided printing process can be preformed more easily.