An image forming apparatus able to operate in a rewritable print mode wherein images are formed with a decolorable colorant, comprising: an image data acquiring unit that acquires image data of an image to be formed on an unused or a reused sheet in the rewritable print mode; a setting information determining unit which determines whether an unused or reused sheet is to be used; an identification information acquiring unit that generates in the rewritable print mode and upon determination that an unused sheet is to be used identification information that identifies the sheet on which the image is to be formed; an image forming unit that, in said rewritable print mode and upon determination that an unused sheet is to be used, forms an image based on the image data acquired by the image data acquiring unit on the sheet with a decolorable colorant which becomes colorless by a predetermined chemical reaction and that forms an identification information image based on the identification information on the same sheet with a non-decolorable colorant which does not become colorless by the chemical reaction by which the decolorable colorant becomes colorless; and a storage control unit that, in said rewritable print mode and upon determination that an unused sheet is to be used, stores the identification information and the image data of the image formed on the sheet, on which the identification information image corresponding to the identification information is formed, in a predetermined storage region in a correlated manner, wherein the image forming unit includes: a first image forming unit that is an image forming unit of an electrophotographic method and forms the identification information image on the sheet with the non-decolorable colorant and a second image forming unit that is an image forming unit of an ink jet method and that forms the image on the sheet with the decolorable colorant and images are formed by an ink jet method after images are formed by an electrophotographic method. an image data acquiring unit that acquires image data of an image to be formed on an unused or a reused sheet in the rewritable print mode; a setting information determining unit which determines whether an unused or reused sheet is to be used; an identification information acquiring unit that generates in the rewritable print mode and upon determination that an unused sheet is to be used identification information that identifies the sheet on which the image is to be formed; an image forming unit that, in said rewritable print mode and upon determination that an unused sheet is to be used, forms an image based on the image data acquired by the image data acquiring unit on the sheet with a decolorable colorant which becomes colorless by a predetermined chemical reaction and that forms an identification information image based on the identification information on the same sheet with a non-decolorable colorant which does not become colorless by the chemical reaction by which the decolorable colorant becomes colorless; and a storage control unit that, in said rewritable print mode and upon determination that an unused sheet is to be used, stores the identification information and the image data of the image formed on the sheet, on which the identification information image corresponding to the identification information is formed, in a predetermined storage region in a correlated manner, wherein the image forming unit includes: a first image forming unit that is an image forming unit of an electrophotographic method and forms the identification information image on the sheet with the non-decolorable colorant and a second image forming unit that is an image forming unit of an ink jet method and that forms the image on the sheet with the decolorable colorant and images are formed by an ink jet method after images are formed by an electrophotographic method. a first image forming unit that is an image forming unit of an electrophotographic method and forms the identification information image on the sheet with the non-decolorable colorant and a second image forming unit that is an image forming unit of an ink jet method and that forms the image on the sheet with the decolorable colorant and images are formed by an ink jet method after images are formed by an electrophotographic method.