PURPOSE: To provide the title method enabling system simplification, so designed that in warp breakage, the end of the warp broken is vertically moved along dents to detect the breaking point without the need for separating the normal warps adjacent thereto, and the corresponding dent position is detected.

CONSTITUTION: When warp breakage occurs during weaving, suction pipe 54 is moved between a heald 4 and reed 6 from the waiting position to the position of the warp, broken in response to a command from a weaving controller based on the position information of the weaving width direction for a falling dropper in compliance with the program set in advance. A suction airflow is then generated at the opening, turning downward, of the suction pipe 54 and the end of the warp broken on the winding side is drawn into the pipe, and the output signal as the result of its confirmation by a yarn sensor 57 is inputted into the controller, followed by moving a position sensor 70 close to the front side of the reed 6 from one of the weaving width ends to the other, thus detecting the dent position corresponding to said warp broken.