PURPOSE: To insert weld zone indicating paper and to roll it in a coil safely and automatically by forecasting the position of insertion of indicating paper of a tension reel at the time of completion of welding when inserting weld zone indicating paper to a hoop steel coil, and making the indicating paper holding and inserting device waiting at the position of insertion.

CONSTITUTION: A hoop steel 2 from a pay-of reel 4 is welded by a welding machine 8, and after passing through a processing tank 12, taken up on a tension reel 26 as a large-diameter coil. In this case, the kind, the plate width, the plate thickness etc. of the hoop steel 2 are inputted to a terminal equipment 38. A coil diameter operating circuit 40 receives a welding completion signal of the hoop steel 2 and calculates the coil diameter D when the weld zone is wound, and a position adjusting circuit 44 calculates the amount of descent of the indicating paper inserting device 37 from the value of D and lowers the device, and then moves said hoop in the direction of coil width to wait it at the position of insertion. An insertion timing operating circuit 46 operates the time of insertion and inserts the indicating paper after the specified time that the weld zone is taken up on the tension reel 26 and makes the paper rolled in.