An apparatus for producing a carbon nanotube fiber, comprising: a vertical reactor having a reaction zone; a concentric double-pipe inlet tube disposed on top of the reaction zone and consisting of an inner pipe through which a spinning feedstock comprising a spinning solution and a first gas is introduced into the reaction zone, further comprising a supply unit for supplying the spinning solution to the inner pipe of the inlet tube, a supply unit for supplying the first gas to the inner pipe of the inlet tube,wherein the spinning solution supply unit comprises a mixing unit where a catalyst or a catalyst precursor is dispersed in a liquid carbon compound to prepare the spinning solution, and a transfer pump for supplying the spinning solution from the mixing unit to the inner pipe of the inlet tube; and an outer pipe defining a concentric annular portion surrounding the inner pipe and through which a second gas is introduced into the reaction zone, wherein an annular opening through which the outer pipe is in communication with the reaction zone is spaced apart from the inner pipe through an annular portion, wherein the annular opening is separated from an opening, through which the inner pipe is in communication with the reaction zone, through an annular thermal insulator positioned between the inner pipe and the outer pipe, and a supply unit for supplying the second gas to the outer pipe of the inlet tube; heating means for heating the reaction zone; and a discharge unit disposed under the bottom of the reaction zone to discharge a carbon nanotube fiber therethrough wherein the spinning feedstock entering the reaction zone through the inner pipe of the inlet tube is carbonized and graphitized while flowing from the top to the bottom of the reaction zone to form a carbon nanotube fiber consisting of a continuous sock of carbon nanotubes and wherein the second gas entering the reaction zone through the outer pipe of the inlet tube forms a gas curtain surrounding the circumference of the continuous sock of carbon nanotubes while flowing from the top to the bottom of the reaction zone. a vertical reactor having a reaction zone; a concentric double-pipe inlet tube disposed on top of the reaction zone and consisting of an inner pipe through which a spinning feedstock comprising a spinning solution and a first gas is introduced into the reaction zone, further comprising a supply unit for supplying the spinning solution to the inner pipe of the inlet tube, a supply unit for supplying the first gas to the inner pipe of the inlet tube,wherein the spinning solution supply unit comprises a mixing unit where a catalyst or a catalyst precursor is dispersed in a liquid carbon compound to prepare the spinning solution, and a transfer pump for supplying the spinning solution from the mixing unit to the inner pipe of the inlet tube; and an outer pipe defining a concentric annular portion surrounding the inner pipe and through which a second gas is introduced into the reaction zone, wherein an annular opening through which the outer pipe is in communication with the reaction zone is spaced apart from the inner pipe through an annular portion, wherein the annular opening is separated from an opening, through which the inner pipe is in communication with the reaction zone, through an annular thermal insulator positioned between the inner pipe and the outer pipe, and a supply unit for supplying the second gas to the outer pipe of the inlet tube; heating means for heating the reaction zone; and a discharge unit disposed under the bottom of the reaction zone to discharge a carbon nanotube fiber therethrough wherein the spinning feedstock entering the reaction zone through the inner pipe of the inlet tube is carbonized and graphitized while flowing from the top to the bottom of the reaction zone to form a carbon nanotube fiber consisting of a continuous sock of carbon nanotubes and wherein the second gas entering the reaction zone through the outer pipe of the inlet tube forms a gas curtain surrounding the circumference of the continuous sock of carbon nanotubes while flowing from the top to the bottom of the reaction zone.