The present invention relates to a method of locating a slit between the dents (61) of the reed (6) of a loom corresponding to a broken warp (1) and to an apparatus for positioning a threading device at a position corresponding to the slit between the dents (61) corresponding to the broken warp (1). The broken warp (1) or a normal warp (1) in a specific relation with the broken warp (1 ) is detected by a yarn sensor (22), the position of a slit between the dents (61) corresponding to the broken warp (1) or that of the normal warp (1) is determined on the basis of the distance traveled by the yarn sensor (22) from its standby position, and a threading device (31) is positioned at a position corresponding to the slit between the dents (61) corresponding to the broken warp (1) on the basis of the distance traveled by the yarn sensor (22).