The invention provides a method and a device capable of precisely and simply extracting data used for abnormality determination and life diagnosis of a drive system of an industrial robot while executing a normal action program. Regarding a torque signal Tf outputted from a motor driver for controlling a motor in accordance with a position command Xs generated based on an operation program of a robot to the motor, a highpass filter is applied after gravity compensating torque and interference torque due to other shafts of the robot are removed from the torque signal Tf, and an abnormality in a reducer is determined based on an extracted oscillating component of the reducer.