PURPOSE: To provide the microprocessor monitoring system having high reliability at the time of detecting an abnormal state, with regard to a system for monitoring normality of a microprocessor.

CONSTITUTION: With respect to a microprocessor 1, a monitoring part 4 having a first glag 2 and a second flag 3 is provided. The monitor part 4 sets '1' to a first flag 2 in a prescribed period, and also, the microprocessor 1 reads timely a first flag 2, and when it is '1', '1' is set to a second flag 3 and '0' is set to a first flag 2, and when a first flag 2 is '0', '0' is set to a second flag 3. In such a state, when the monitoring part 4 detects a fact that the time when a first flag 2 or a second flag 5 is exceeds a prescribed time, normality of the microprocessor is monitored by resetting the microprocessor 1.