An abnormality monitoring circuit of an ECU includes a microcomputer, a reset circuit that resets the microcomputer, a monitor circuit that monitors the operation of the microcomputer, and an output circuit that activates an external actuator. The monitor circuit has an abnormality decision signal output section that outputs an abnormality decision signal to the output circuit when not being able to confirm that an output of a normal monitor signal of the microcomputer has occurred within an abnormality decision time. The monitor circuit has a reset decision signal output section that outputs a reset decision signal to the reset circuit when not being able to confirm that an output of the normal monitor signal of the microcomputer has occurred within a BIST (Built In Self Test) completion time of the microcomputer and a reset decision time set to a time longer than the abnormality decision time.