Provided herein is an image forming apparatus, comprising: a consumable unit where a CRUM (Customer Replaceable Unit Monitoring) chip is mounted; and a main body configured to perform at least one of a first authentication and a second authentication of the consumable unit, when the consumable unit is mounted, wherein the main body comprises: a main controller for performing the first authentication according to firmware stored in the image forming apparatus; and an authentication controller for using at least one ASIC (Application Specific Integrated Circuit) to perform the second authentication of the consumable unit. Accordingly, it is possible to effectively authenticate a consumable unit even when the image forming apparatus is hacked.