One aspect of the instant disclosure is to provide a sensorless adaptive safety actuator. The safety actuator comprises a driving unit, a transmission unit coupled to the driving unit, and an output unit coupled to the transmission unit. The transmission unit comprises a load-adaptable retracting mechanism. When the output unit experiences a mechanical load exceeding a critical value, the load-adaptable retracting mechanism causes the transmission unit to decouple from the driving unit. Thus, responding to an accident where the impact on the output unit causes a force/torque overload, the instant safety actuator is capable of effectively stopping the force/torque transmission to the work output device without the use of active sensors.