PURPOSE: To produce steel nets for ferro-concrete wide and flat in the lengthwise and breadthwise directions at high efficiency, almost automatically, by contacting the protruding parts of steel bar bent in zigzag form at specified pitch and angle, and sequentially welding electrically up to two positions.

CONSTITUTION: A bar material passed through a bar material supply process 3 and straightening process 4 is bent in zigzag form at specified pitch and angle in a process 5. The bent bar material is sent into a welding process 6 containing plural squeeze roll stands, and is quided so that the peak of adjacent bending material peak may contact with the bottom of this bending material. Then two welding parts each are sequentially heated and welded by welding current from a welding power source 6'. That is, in part of the net, high frequency current is passed through chips 10 provided in the central parts 9, 9' between contact parts 8, 8' of the peak of bending material and the bottom of other material. As a result, a high resistance heat is generated in the contact parts 8, 8', and the parts 8, 8' are pressed in the direction of the arrow when reaching the welding temperature, thereby finishing the welding.