Abstract: In a teach-in operation, the working procedure is memorized in an industrial robot in advance of the actual working operation, and the teaching is accomplished by manually guiding the tracing tip of the robot arm along a desired path. The teach-in method comprises the step of attaching, to the end of the arm, the tracing tip having at least a displacement pulse oscillator, which consists of a projector and a phototransistor, and a roller provided with gaps such as holes or slits, the projector and phototransistor being arranged in concentric positions with respect to the respective gaps of the roller so as to form an optical axis between the two optical elements. The tracing tip is then moved along a desired path, so that the location signal of the tracing tip may be obtained by the displacement pulse oscillator, whenever the roller is rotated a certain distance, as a result of the movement of the tracing tip, and such a location signal is memorized in a memory.