The post-processing apparatus 16 includes a crease forming device 52 that performs a crease forming process on a sheet, and a folding device 54 that performs a folding process on the sheet. The position of the crease 70 formed by the crease forming device 52 may deviate from a desired position. Therefore, it is necessary to correct the position where the crease is formed by the crease forming device 52. In the image forming apparatus 10 according to the exemplary embodiment of the present disclosure, the sheet P on which the crease 70 is formed by the crease forming device 52 is read twice by the image reading apparatus 12, and the image processing apparatus 14 specifies a position of the crease based on first image information and second image information obtained by reading. The specified position of the crease or the amount of deviation between the specified position of the crease and the desired position of the crease is sent to the crease forming device 52, and the crease forming device 52 corrects the position where the crease is formed in the sheet based on the information. As a result, the position of the crease 70 formed on the sheet P by the crease forming device 52 thereafter becomes a desired position or closer to the desired position.