Disclosed is an error detection method of fail safe software, the method including outputting a pulse signal according to an operation state of fail safe software monitoring a fail safe function of a motor control device; determining presence or absence of an error of the fail safe software using a frequency of the pulse signal; and controlling an output of the motor control device based on the presence or absence of the error of the fail safe software. Accordingly, even though whether the motor control device is in an abnormal state is not determined due to an error of the fail safe software, it is possible to prevent excessive motor torque from occurring.