To detect an entangled part of a wire rod supplied to a work machine, without generating wire breakage and elongation, and without giving an overload burden to the work machine working the wire rod.

This device is provided with a limit switch 4 and a deflection plate 2 having a slit 2a of desired size to be mounted in a mounting base 1 so as to press the limit switch 4 by a hinge 3 with spring. Here, a wire rod 5 is inserted through the slit 2a and run in an opposite direction to a press direction, and by deflection of the deflection plate 2 when an entangled part 5a of the wire rod 5 passes through the slit 2a, the limit switch 4 is operated, to detect the entangled part 5a of the wire rod 5.