In an image processing apparatus, an HDD stores registration data, an operation unit receives an instruction requesting erasure of the registration data, and a control unit erases the registration data and restricts operations of the image processing apparatus in response to the instruction. Further, the HDD stores unique information unique to the image processing apparatus and changeable information that is changed in response to the erasure of registration data. If it is determined that a cancellation key generated by a management server and received by the operation unit is a cancellation key corresponding to the unique information and the changeable information, the control unit cancels the operation restriction of the image processing apparatus.