A welding jig device used for forming a part by welding a plurality of members together, wherein the part comprises a desired welded portion, the desired welded portion consists of an annular closed path, the desired welded portion comprises a first portion and a second portion, the first portion and the second portion form the annular closed path; the welding jig device comprising: a jig on one side including a joint face on the one side and an opening on the one side, the joint face on the one side being adapted to contact one of faces exposed on outer surface sides of the plurality of members that are overlaid one on top of the other, the opening on the one side corresponding to the first portion of the desired welded portion of the part, and a jig on another side including a joint face on the other side and an opening on the other side, the joint face on the other side being adapted to contact another face of the faces exposed on the outer surface sides of the plurality of members, the opening on the other side corresponding to the second portion of the desired welded portion of the part and not corresponding to the opening on the one side; wherein the opening on the one side is configured that the first portion is formed through the opening on the one side by the welding, and the opening on the other side is configured that the second portion is formed through the opening on the other side by the welding. wherein the part comprises a desired welded portion, the desired welded portion consists of an annular closed path, the desired welded portion comprises a first portion and a second portion, the first portion and the second portion form the annular closed path; the welding jig device comprising: a jig on one side including a joint face on the one side and an opening on the one side, the joint face on the one side being adapted to contact one of faces exposed on outer surface sides of the plurality of members that are overlaid one on top of the other, the opening on the one side corresponding to the first portion of the desired welded portion of the part, and a jig on another side including a joint face on the other side and an opening on the other side, the joint face on the other side being adapted to contact another face of the faces exposed on the outer surface sides of the plurality of members, the opening on the other side corresponding to the second portion of the desired welded portion of the part and not corresponding to the opening on the one side; wherein the opening on the one side is configured that the first portion is formed through the opening on the one side by the welding, and the opening on the other side is configured that the second portion is formed through the opening on the other side by the welding. a jig on one side including a joint face on the one side and an opening on the one side, the joint face on the one side being adapted to contact one of faces exposed on outer surface sides of the plurality of members that are overlaid one on top of the other, the opening on the one side corresponding to the first portion of the desired welded portion of the part, and a jig on another side including a joint face on the other side and an opening on the other side, the joint face on the other side being adapted to contact another face of the faces exposed on the outer surface sides of the plurality of members, the opening on the other side corresponding to the second portion of the desired welded portion of the part and not corresponding to the opening on the one side; wherein the opening on the one side is configured that the first portion is formed through the opening on the one side by the welding, and the opening on the other side is configured that the second portion is formed through the opening on the other side by the welding.