PURPOSE: To realize the restart of a CPU, by executing a useless instruction when the CPU has a fault.

CONSTITUTION: When a CPU1 runs away and tries to fetch a memory space which does not exist actually, a signal of H level is delivered from an OR gate 4. As a result, a memory 3 is chip-selected and the data is delivered to data buses D0WD7 to execute the 1-operation of an 1-byte instruction. The CPU1 reads this data, and the contents of a program counter to count the address of the memory 3 in the CPU1 is increased. The execution of the 1-operation is repeated to repeat the increment of the program counter. Meanwhile the youngest address of an existing memory is fetched. The area of this address is written in a prescribed restart routine, and as a result the execution is possible again to a normal program for the CPU1.