A processor and a control method thereof are processed. The processor includes an instruction fetch module configured to receive a first instruction of an interrupt service routine without backup of data stored in a register in response to processing of the interrupt service routine being requested, a detecting module configured to analyze the received first instruction to determine whether the data stored in the register needs to be changed, an instruction generating module configured to generate a second instruction for storing data in a temporary memory when the stored data is initially changed, an instruction selecting module configured to sequentially select the generated second instruction and first instruction; and a control module configured to perform the second instruction and the first instruction.