A power failure section can be accurately detected without depending on a loaded state and application of voltage to the overhead power line can be stopped in a short time when a power failure is detected. An electric car controller includes an overhead power line voltage detector, a band-pass filter for detecting a ripple component included in the detected overhead power line voltage, a comparator for comparing the level of the detected ripple component with a predetermined reference value Vref1, a rheotome control circuit which judges that a power failure has occurred if the ripple component is judged to be smaller than the reference value Vref1 and disconnects the overhead power line from an inverter, a second comparator for comparing the level of the ripple component with a reference value Vref2 larger than the reference value Vref1, and a control circuit which operates if the ripple component is judged to be smaller than the reference value Vref2 to suppress the increase of the overhead power line voltage.