Abstract: A control device of an electric power steering device includes an arithmetic processing device having a comparison unit, a failure diagnosis unit, and a drive control unit. The comparison unit compares a difference between a first output signal output from a first sensor and a second output signal output from a second sensor with a first threshold value to determine a magnitude relationship, and compares a difference between the first output signal and a third output signal output from a third sensor with a second threshold value to determine a magnitude relationship. Based on a result of the comparison unit, the failure diagnosis unit identifies one abnormal sensor among the first, second and third sensor. Using output values from two normal sensors that are not identified as abnormal sensors among the first, second and third sensor, the drive control unit generates a drive control signal for driving an electric motor.