PURPOSE: To prevent the breakage of warp, etc., caused by the breakage of rapier band by detecting holes or distance between holes for the engagement of rapier band and comparing the detected result with the abrasion limit of the hole.

CONSTITUTION: Holds or distance between holes for the engagement of a rapier band 3 are detected with a sensor 11 and the detected value is compared by a comparator with a standard value transmitted from a standard setting device which outputs a standard signal corresponding to the abrasion limit of the hole of the rapier band. When the order of the levels of the detected value and the standard value is reversed, a comparison signal is outputted to activate an alarm.