A MOD_SAT instruction indicating that a 16 bit saturation is to be carried out with respect to the operation of one of instructions executed in parallel is placed in the left container and an ADD instruction is placed in the right container. When the instruction decode unit decodes these instructions, the instruction decode unit indicates that the instruction execution unit executes the ADD instruction accompanying a saturation process. Accordingly, the operation of a great number of instructions can be modified by combining instructions and, therefore, the basic instruction length can be made short and it becomes possible to increase the code efficiency.