When a normal interrupt occurs, data of processor operation before the normal interrupt are held in a normal return address register (452), a normal previous state register (453), and a normal factor register (454). When a break-interrupt occurs, data of processor operation before the break-interrupt is held in another break return address register (455). Hence, a break-interrupt can occur even within an interrupt inhibition period by a normal interrupt. Besides, when a break-interrupt occurs, the break-interrupt state is set in a flag register (456). By referring to the flag register (456) in executing an interrupt return instruction, the operation data before the break-interrupt or before the normal interrupt can accurately be restored.