PURPOSE: To obtain the title device in which a sensor having an evaluation circuit for comparing and judging thickness of yarn based on the output and wind-up operating circuit and cutter operating circuit in which either one circuit is operated by the above-mentioned evaluation is attached and reduced in abnormal take up.

CONSTITUTION: A sensor 2 of device for judging thickness of yarn is provided immediately above yarn-ending device body 1 and in case of yarn ending, suction mouth 10 is turned downward and yarn end is sucked from a package 11 and pulled yarn end is pulled up and induced into yarn-ending device body 1 and a lever 12 is turned and yarn Y is pushed into a yarn leading groove 9 of sensor 2 and thickness of yarn Y is evaluated by evaluation circuit 4 for comparing and judging thickness of yarn Y based on the output and either one of wind-up operation circuit 7 and cutter operation circuit 8 is operated by the evaluation to constitute a yarn ending device for double yarn. The yarn ending device prevents occurrence of abnormal yarn ending.