PURPOSE: To improve productivity, to detect forming defects of tube stock and to simplify correction by providing a shield cover for covering only a local part between the welding equipment around the weld zone and a tube stock minimizing the shielded space around the weld zone and decreasing the concentration of oxygen inside the space in a short time.

CONSTITUTION: In this shielding device 20, a shield cover 22 is attached to the roll stand 100 of a squeeze roll 12, and only a local part (around a contactor 11 and the squeeze roll 12A) between the welding equipment 10 around the weld zone and a tube stock A is covered with the cover. Incidentally, 101 is the roll chock of an upper roll 12A. In addition, the device is provided with a shield rubber 102A in the part that comes into contact with the tube stock 1A and also a shield rubber 102B in the part with the welding equipment 10. Furthermore, the welding equipment 10 is capable of moving vertically between the lowered position with welding and the raised position without welding by means of an elevating part 13, and the contactor 11 is brought into contact with the tube stock 1A at the lowered position, thereby covering it with the shield cover 22 at this position.