A method of determining a failure of a robot, comprising: a step of determining while a robot is operating whether or not a motor output torque moving average value, which is a moving average value of N, N being a positive integer, pieces of motor output torque average values, exceeds a first failure determination reference value, which is a value produced by adding a first given value to a motor output torque moving average reference value obtained from the given N pieces of motor output torque average values; a step of determining while a robot is operating whether or not an external force torque moving average value, which is a moving average value of N pieces of external force torque moving values, exceeds a second failure determination reference value, which is a value produced by adding a second given value to an external force torque moving average reference value obtained from the given N pieces of external force torque average values; a step of determining a failure of the robot if the motor output torque average value exceeds the first failure determination reference value and the external force torque moving average value exceeds the second failure determination reference value; and wherein the motor output torque moving average value is set when the difference between each of NN, NN being a positive integer, pieces of motor output torque average values and the motor output torque moving average value is smaller than a given value preliminarily determined, as a motor output torque moving average reference value, and the external force torque moving average value is set at this moment as an external force torque moving average reference value. a step of determining while a robot is operating whether or not a motor output torque moving average value, which is a moving average value of N, N being a positive integer, pieces of motor output torque average values, exceeds a first failure determination reference value, which is a value produced by adding a first given value to a motor output torque moving average reference value obtained from the given N pieces of motor output torque average values; a step of determining while a robot is operating whether or not an external force torque moving average value, which is a moving average value of N pieces of external force torque moving values, exceeds a second failure determination reference value, which is a value produced by adding a second given value to an external force torque moving average reference value obtained from the given N pieces of external force torque average values; a step of determining a failure of the robot if the motor output torque average value exceeds the first failure determination reference value and the external force torque moving average value exceeds the second failure determination reference value; and wherein the motor output torque moving average value is set when the difference between each of NN, NN being a positive integer, pieces of motor output torque average values and the motor output torque moving average value is smaller than a given value preliminarily determined, as a motor output torque moving average reference value, and the external force torque moving average value is set at this moment as an external force torque moving average reference value.