PURPOSE: To detect an object to be touched and detected even if this object is non-conductive or there is a paint, clothes, or the like on the surface of the object, by detecting a flexure of a touch bar, namely, a wire, which is generated when the object is touched, as a strain of a flat spring.

CONSTITUTION: When a welding wires 2 touches an object 1 to be welded, a bend is generated in a flat spring 7, which is preliminarily brought into contact with the welding wire 2, by the flexure of the wire 2, and a strain is generated in the flat spring 7. This strain is detected by strain gauges 11 and 12 to detect that the object 1 to be welded and the welding wire 2 are brought into contact with each other. A protective plate 10 shields the flat spring to protect the flat spring 7 from sputter, heat, dust, etc. for welding and consists of metallic or heat-resisting materials. The number of flat springs 7 may be increased. Both strain gauges 11 and 12 are not always necessary, and the strain of the flat spring 7 can be detected only by the strain gauge 11 or 12. Positions to which these strain gauges are stuck may be changed to another positions of the flat spring 7.