In a voltage booster apparatus, a charge control transistor is turned on to charge a coil output capacitor and a booster output capacitor and then turned off, thereby confirming rise of a coil output voltage and a booster output voltage. A power supply relay is turned on to restore a booster operation thereby to check rise of the booster output voltage. If both of a step-up FET and a step-down FET are not in short-circuit failure, ON state of the power supply relay is fixed thereby to restore a power steering system operation.