<p>A program data area 38 storing program data is provided in an internal memory unit that a control circuit 31 of a CPU 3 can directly red from. The program data is constituted by instructions each comprising an instruction information part and an operand (i.e., a complementary information part) for use in execution of this instruction information part. The program data area 38 comprises a plurality of 24-bit data areas each having an address indicative thereof. One instruction is stored in one data area such that the instruction information part resides at the beginning of the data area.</p>
