This invention provides a sealing apparatus for a twin-roll casting machine, comprising a transition piece (4) located above a molten metal pool (6) formed between cooling rolls (1), self-rotatable cylindrical brushes (7) extended in the same direction as the cooling rolls (1) and abutted against the whole length in the direction of a shaft line on the outer circumferential surface of the coolingrolls (1) from the opposite side of the molten metal pool (6) below the transition piece (4), a first cow ring (9) covering the outer circumferential surface, of the cooling roll (1), in its part from the transition piece (4) to the brush (7), a second cow ring (10) surrounding the brush (7) in its part not abutted against the cooling roll (1), a third cow ring (11) covering the cooling roll (1) in its part below the brush (7), and an outlet (8) for feeding a seal gas (S) into between the transition piece (4) and the cooling roll (1). A part from the outlet (8) to the outlet part of the thirdcow ring (11) is filled with the seal gas (S) fed through the outlet (8).