To provide a device for preventing blow off of a molten metal, capable of preventing contact surfaces of dies of a vacuum valve from opening each other by using the molten metal to be force fed into the dies, preventing of the blow off of the molten metal, and eventually realizing smooth production.

The device 105 for preventing blow off of a molten metal includes a pair of a first die 110 and a second die 130 constituting a vacuum valve 100 by being engaged with each other. The first die is provided with: a first type abutment surface 154 abutting on a back surface 112 of a contact surface of the second die; and a first molten metal contact surface 158 on which the molten metal 14 force fed into a mold 10 mounted with the vacuum valve abuts. A first material 150 is provided in order to press the first die at the first type abutment surface when the first molten metal reaches the first molten metal contact surface. The second die is provided with: a second die abutment surface 164 abutting on a back surface 132 of the contact surface with the first die; and a second molten metal abutment surface 168 on which the molten metal force fed into the mold abuts. A second member 160 is provided to press the second die with the second die abutment surface when the molten metal abuts on the second molten metal abutment surface.