An image forming apparatus, comprising: a main body portion of the image forming apparatus; and at least one replaceable unit which is mountable to the main body portion of the image forming apparatus to execute an image forming operation, wherein the main body portion of the image forming apparatus comprises a main controller to control operations of the image forming apparatus, wherein the at least one replaceable unit comprises: a memory unit to store information regarding the replaceable unit and to store an initialization program for performing an initialization; and a central processing unit which manages the memory unit using an operating system of the of the CPU, wherein, when the replaceable unit is mounted to the image forming apparatus, the CPU is initialized using the initialization program separately from the main controller, the CPU being configured to access the information stored in the memory unit and to perform authentication and cryptographic data communication with the main controller of the image forming apparatus by executing a cryptographic algorithm selected from a plurality of cryptographic algorithms wherein the memory unit of the replaceable unit stores the operating system to be executed by the CPU and the initialization program is included in the operating system, the operating system of the CPU is different from an operating system of the main controller, characterised in that the memory unit has a software structure including a memory recovery region, and the CPU backs up previously recorded values within the memory recovery region and sets a start flag when a data writing operation for the memory unit is executed, and the CPU checks changed values of the start flag when a specific event happens, and then determines whether the changed values are rolled back to the previous recorded values. a main body portion of the image forming apparatus; and at least one replaceable unit which is mountable to the main body portion of the image forming apparatus to execute an image forming operation, wherein the main body portion of the image forming apparatus comprises a main controller to control operations of the image forming apparatus, wherein the at least one replaceable unit comprises: a memory unit to store information regarding the replaceable unit and to store an initialization program for performing an initialization; and a central processing unit which manages the memory unit using an operating system of the of the CPU, wherein, when the replaceable unit is mounted to the image forming apparatus, the CPU is initialized using the initialization program separately from the main controller, the CPU being configured to access the information stored in the memory unit and to perform authentication and cryptographic data communication with the main controller of the image forming apparatus by executing a cryptographic algorithm selected from a plurality of cryptographic algorithms wherein the memory unit of the replaceable unit stores the operating system to be executed by the CPU and the initialization program is included in the operating system, the operating system of the CPU is different from an operating system of the main controller, characterised in that the memory unit has a software structure including a memory recovery region, and the CPU backs up previously recorded values within the memory recovery region and sets a start flag when a data writing operation for the memory unit is executed, and the CPU checks changed values of the start flag when a specific event happens, and then determines whether the changed values are rolled back to the previous recorded values. a memory unit to store information regarding the replaceable unit and to store an initialization program for performing an initialization; and a central processing unit which manages the memory unit using an operating system of the of the CPU, wherein, when the replaceable unit is mounted to the image forming apparatus, the CPU is initialized using the initialization program separately from the main controller, the CPU being configured to access the information stored in the memory unit and to perform authentication and cryptographic data communication with the main controller of the image forming apparatus by executing a cryptographic algorithm selected from a plurality of cryptographic algorithms wherein the memory unit of the replaceable unit stores the operating system to be executed by the CPU and the initialization program is included in the operating system, the operating system of the CPU is different from an operating system of the main controller, characterised in that the memory unit has a software structure including a memory recovery region, and the CPU backs up previously recorded values within the memory recovery region and sets a start flag when a data writing operation for the memory unit is executed, and the CPU checks changed values of the start flag when a specific event happens, and then determines whether the changed values are rolled back to the previous recorded values.