Abstract: An apparatus for controlling gas layer thickness on the surface of casting rolls in a twin roll strip caster includes: a pair of chambers fixedly mounted on both lateral portions of the meniscus shield in a width direction of a strip; blocking units for blocking introduction of pollutants into the molten metal pool, wherein each of the blocking units includes front and rear barrier members which are mounted on each of the chambers and in close contact with an outer periphery of each casting roll and a blower for injecting inert gas toward the outer periphery of each casting roll; operating units for adjusting the thickness and the width of gas layers at both ends of the casting rolls, wherein each of the operating units includes suction lines connected with each chamber to transmit a suction force to ends of each casting roll and a pair of movable plates slidably assembled to both side portions within each chamber for being reciprocated by movable members; and a control unit for controlling the suction force