A main microcomputer abnormality determination section checks whether or not a voltage value of Vcc based on digital data output from a main microcomputer analog-to-digital converter is equal to or higher than a threshold value to thereby perform abnormality determination for the main microcomputer analog-to-digital converter and Vref. A sub microcomputer abnormality determination section checks whether or not the voltage value of Vcc is equal to or higher than a threshold value based on digital data output from a sub microcomputer analog-to-digital converter to thereby perform abnormality determination for the sub microcomputer analog-to-digital converter and Vref. An abnormality identifying section identifies an abnormality occurring site by using both results of the abnormality determination performed by the main microcomputer abnormality determination section and the sub microcomputer abnormality determination section.