PURPOSE: To detect exactly the presence or absence of a wire with simple constitution, by turning a lever by the tension of the wire and operating a switch when the wire on a reel runs out when the initial coiling end of the wire is fixed to the reel.

CONSTITUTION: The initial coiling end of a wire 23 is hooked in the hole 24b of a reel 24, and the wire 23 is coiled on the core 24a of the reel 24. The wire 23 is fed through a leading-out port 25 to the outside. A detector having a lever 15 is disposed between the center (o) of the reel 24 and the port 25. When the wire 23 is fed, the wire 23 does not contact the roll 17 of the lever 15 from the outermost layer 26 of the wire 23 on the reel 24 up to the innermost layer 27. When the wire 23 is completely run out and the wire 23 is pulled on the line connecting the center (o) of the reel, the hole 24b and the port 25, the wire moves the lever 15 to the position of an alternate long and two short dashes line. Then the projection 15a of the lever 15 is disengaged from the operating lever 14a of a microswitch 14, by which the microswitch 14 is turned off and the welding is stopped or an alarm is emitted.