To provide an image output device for outputting images in an appropriate direction in a surface and a back surface of a printing paper.

When the printing condition is input and fixed, this image output device checks whether size of the printing paper O is post card size or not, and in the case of YES, displays a surface and back surface specifying screen, and when the surface or the back surface is specified as a printing surface, the image output device checks which one of the surface or the back surface is specified. The image output device operates a surface mark detecting sensor or a back surface mark detecting sensor to check whether a postage stamp exists at the postage stamp position or not, and in the case of YES, the image output device performs the normal printing processing. In the case of NO, the image output device judges that a surface of the post card set in a paper tray and a surface of the printing image do not coincide with each other or that direction (vertical direction) of the post card set in the paper tray is not appropriate, and stops the printing processing to the post card.