PURPOSE: To reactivate a processor in a short time by defining the fact that a timer is not reset within a time preliminarily set by an access monitoring part as the generation of a bus lock, turning-on a reset line, and reactivating the processor.

CONSTITUTION: A timer 3 which turns-on a reset line 2 of a processor 1, and reactivates the processor 1 when the timer is not reset within the preliminarily set time, and an access monitoring part 5 which monitors the access state of a memory access line 4 of the processor 1, and resets the timer 3 at the time of detecting the access, are provided. Then, when the timer 3 is not reset within the time preliminarily set by the access monitoring part 5, it is defined as the generation of the bus lock, the reset line 2 is turned-on, and the processor 1 is reactivated. Thus, the processor is reactivated in the short time as hardly noticed from the outside, even at the time of the generation of the bus lock.