A power supply circuit for operating an emergency stop device for an elevator employs a charging capacitor for activating an actuator through discharge. Further, a failure detector which checks loss in the capacitance of the charging capacitor is electrically connected to the power supply circuit. The failure detector has a memory storing the upper and lower limits of charging time when the charging capacitor is normal and has a CPU capable of measuring charging time of the charging capacitor and deciding whether or not the charging time falls between the upper and lower limits. The CPU judges that the capacitance of the charging capacitor is not lost when the charging time falls between the upper and lower limits. |