1. An image forming apparatus comprising; a storage region that stores an information regarding an image formed on a sheet in connection with an identification information that identifies a sheet on which an image is formed; an identification information image reading unit that reads an identification information image which is formed on a sheet and is based on the identification information; and a decoloring unit to execute a decoloring process on a sheet on which an image is formed with a decolorable colorant, which decolors the image formed on a sheet based on a reading result of the identification information image reading unit.