A method for removing slag comprises: preparing a filter 21 of heat-resistant porous ceramics, which passes a molten metal and catches slag, liquidizing metal material to form a molten metal A on which slag is floating; and traveling filter 21 along a surface of the molten metal A and removing slag. And a device for removing slag comprises: a filter 21 of heat-resistant porous ceramics, which passes a molten metal and catches slag; and a driving device for traveling filter 21 along a surface of the molten metal on which slag is floating and removing slag.