PURPOSE: To execute a compressed program without decoding it beforehand.

CONSTITUTION: When the code of the compressed program stored in an address outputted from an address bus 109 is read from a data bus 110, it is tentatively stored through a bus input/output control unit 102 in a prefetch 104. The code is inputted to an expansion unit 105 and restored to an original program code. The program code is inputted by a synchronous processing unit 106 to an instruction interpretation/instruction control/execution control unit 107 and executed. The result is inputted through a control signal 112 and a memory management unit 108 or through an internal bus 113 to the bus input/output control unit 102 and outputted from the control signal 111, the address bus 109 and the data bus 110. Also, whether or not the code is a compressed code can be judged by providing an instruction discrimination unit before an expansion processing unit.