PURPOSE: To immediately transfer control to an error processing program even when an error occurs in a program and data in a program unstoring area is recognized erroneously as the program by storing a specific instruction to transfer the control to the error processing program in the (unstored program area.

CONSTITUTION: An instruction (3) which transfers the control to the entry of a (program unstoring area execution error processing) program is stored in the unstored program area (1). Therefore, when the error occurs in the program and a CPU executes the unstored program area (1) erroneously as an instruction, the control is transferred to the unstored program area execution error processing) and fast error countermeasure can be taken since the instruction (3) which transfers the control to the entry of the error processing program, for example, an interrupt instrucction which performs the similar operation as that of an unconditional branch instruction is stored in the unstored program area (1).