A processor includes a storage unit storing an instruction, an instruction extension information register that includes a first area and a second area, an instruction decoding unit that decodes a first prefix instruction including first extension information extending an immediately following instruction written to the first area when the first prefix instruction is executed, and that decodes a second prefix instruction including the first extension information and a second extension information extending an instruction immediately following two instructions of the second prefix instruction, an instruction packing unit that generates a packed instruction including at least one of the first prefix instruction or the second prefix instruction, and the instruction immediately following the first prefix instruction or the second prefix instruction when the instruction decoding unit decodes the first prefix instruction or the second prefix instruction, an instruction execution unit that executes the packed instruction generated by the instruction packing unit.