An emergency stop system for an elevator includes a state sensor for detecting an operation of a car, a brake device for braking the car, a brake controller for outputting a signal for operating the brake device based on a signal detected by the state sensor, and an uninterruptible power supply device for supplying electric power to the sensor, the brake device, and the controller. The controller has a signal processing/calculating unit for calculating the deceleration of the car based on the signal detected by the sensor, a command value calculating unit for calculating a command value for operating the brake device based on the deceleration of the car calculated by the processing/calculating unit, and a power monitoring device for monitoring state of the uninterruptible power supply device. At least one of the sensor, the processing/calculating unit, and the calculating unit includes independent systems.