Image forming apparatus and image forming method

An image forming apparatus that uses a stackless ADU and executes image formation on both sides of a paper sheet in a facedown mode, comprising:

• confirmation means for confirming, when double-side image formation is to be executed with two paper sheets, image formation on reverse surfaces of which is finished, being stayed in the ADU, whether monochromatic image formation or color image formation is to be executed on an obverse surface of a first paper sheet that is stayed in the ADU and has a reverse surface on which image formation is finished;
• first control means for controlling, when the confirmation means confirms the color image formation to be executed, the image formation on the obverse surface of the first paper sheet that is stayed in the ADU and has the reverse surface on which image formation is finished;
• and
• second control means for controlling, when the confirmation means confirms the monochromatic image formation to be executed, the image formation on a reverse surface of a second paper sheet that is stayed in the ADU.