Abstract: A vacuum shield device of an electron beam welding apparatus including a plate of a rectangular shape formed with a slit for allowing a beam of electrons to pass therethrough, a box-shaped member secured to the undersurface of the rectangular plate with its walls surrounding the slit, and a shield member secured to the outer periphery of the lower portions of the walls of the box-shaped member. The shield member includes a base formed of a heat-resisting and flexible material maintained in pressing engagement with the upper surface of the workpiece by pressing means. The force with which the pressing means forces the base against the workpiece is adjusted by pressure control means. The box-shaped member is formed with a cutout at the lower portion of either end wall.