To prevent spatters flying from dotting part of the other welding gun from infiltrating into a gun body when a movable gun arm is opened.

A sheet cover member 14 is provided in a way that one end part thereof is fixed with a part 15 of the gun body 1 wherein a space is positioned between the fixed gun arm 2 and the movable gun 3 when the movable gun arm 3 is in a closed status, and the other end part with an arm holder 12. In keeping with the opening/closing operation of the gun arm 3, the cover member 14 is developed and folded so that a spatter infiltration path against the gun body 1 is always covered by the member 14 regardless if the gun arm 3 is opened or closed.