There is provided an image forming apparatus capable of realizing a trial printing function that minimizes unnecessary consumption of time and supplies. Images that are inputted are accumulated in a memory. An output mode is set and a setting is made as to whether trial printing is to be carried out in the output mode or not. A CPU provides control to read out a corresponding image from the memory according to the set output mode and form the readout image on a sheet. When it is determined that the trial printing is to be carried out during image formation according to the set output mode, the CPU provides control to set the number of trial print pages according to predetermined conditions and carry out the trial printing for the set number of trial print pages.