1. An image forming apparatus comprising: an input unit having a function of receiving additional input of image data; a storing unit storing the image data input from the input unit; an output unit for performing image output based on the image data stored in storing unit; and, an image display control device, characterized in that the image display control device includes: a function setup controller having a function of setting up image output conditions of an image to be output from the output unit; a display image generator generating a display image based on the image data stored in the storing unit; a display unit having a display screen for displaying the display image generated by the display image generator; and a display controller having a function of displaying the display image on the display unit in preview representation, the function setup controller includes: an image data sheaf forming function of forming a plurality of image data sheaves by additionally inputting the image data multiple times; a section break setup function that, when the image data is additionally input, sets up a section break for creating a section to distinguish the additional input image data to be additionally input, from the precedent image data that has been input already; an image output condition storing function for storing image output conditions set for each of the sections; and, an image output executing function of performing image output in accordance with the setup of image output conditions for each section.