A finishing apparatus of an image forming apparatus and a method for controlling the same are disclosed, in which various block modules performing finishing functions are provided and a user can selectively use any module by detachably fixing the same in a copier. The finishing apparatus includes a paper conveyer module detachably fixed to an image tray module, a mail box module, a finisher module, and a booklet module, the paper conveyer module being detachably fixed in a copier. The paper conveyer module includes a controller sensing whether the respective modules are detachably provided to selectively control functions of the respective modules in accordance with an output signal of the copier. In addition, paper path switch devices provided in the paper conveyer module include a plurality of paper dispensers that dispense papers in three or more directions.