PURPOSE:The title device designed to separate slags with difference in gravity automatically and to take out the slags without stopping the operation of the gasifier, wherein a solenoid pump is provided at the extended molten substance take out complete with a gutter and a weir. CONSTITUTION:The pump is operated to the right by the control unit 9 of the solenoid pump 5 during the operation of the gasifier 1, and the take-out 4 is closed. When the amounts of the mixture of molten iron 2 and slag 3 are increased, the operation direction of the pump is changed over by the unit 9 to make the mixture flow to the gutter 6. The slag 3 floats on the molten iron 2 during the outflow by the difference in gravity, is stopped by the weir 7, then overflown from the weir 7, and discharged from the gutter 6 sideways. The other molten iron 2 is passed under the weir plate 7a, and discharged from the tip of the gutter 6.