Abstract: A robot safety device, which is provided between a drive shaft of a robot and an actuator for driving the drive shaft and prevents unexpected action to a user positioned around the robot, and in which such a possibility that a robot damages a person is detected and the detection is utilized as a trigger to quickly stop the driving force for the robot. The device is provided with a transmission part which transmits to the drive shaft an output from the actuator, an acceleration operation corresponding part which mechanically generates corresponding to the transmission accelerating operation of the transmission part caused by the actuator, regulation auxiliary force for regulating the operation of the transmission part caused by the output from the actuator, and a regulation part which is driven by the regulation auxiliary force generated by the accelerating operation corresponding part and regulates the operation of the transmission part.