To obtain a long radiation shield with rigid welding with less deformation by welding while keeping the inside of coolant path free from invasion of spatters, etc., through communication such coolant paths on the occasion of welding the radiation shields in the axial direction.

In the case of obtaining a long radiation shield, being formed of a double-layered cylinder having an internal cylinder 10 and an external cylinder 11 and having a coolant path 12 in the axial direction to cause the coolant to flow between the welded internal cylinder 10 and the external cylinder 11, by welding the radiation shield in the axial direction, an external diameter of the external cylinder 11 at the area where the coolant path 12 of the radiation shield is provided is partially set larger than the thickness of the internal cylinder 10. The area where there is no coolant path 12 is welded in the total thickness by executing electron beam welding 15 from the external circumference side while the welding power and the radiation time are kept constant. Moreover, the area where the coolant path 12 is provided is welded in such a manner that only the external circumference is welded and thereafter only the internal circumference of the coolant path 12 is welded by the TIG welding method 16.