A refinement apparatus comprising: a container unit having an open upper portion and an inner space in which a melt is refined; a nozzle unit installed on the container unit to blow a gas (g); a camera unit installed above the container unit to photograph a molten steel surface of the melt; and a control unit configured to calculate a size of naked molten steel on the molten steel surface by using a molten steel surface image obtained from the camera unit and installation information and performance information of the camera unit, wherein the installation information comprises an installation height and an installation angle of the camera unit, and the performance information comprises a view angle and a resolution of the camera unit, wherein the molten steel surface image is a single viewpoint molten steel surface image, wherein the control unit comprises: a deriver configured to derive the installation height with respect to the molten steel surface; a first calculator configured to calculate a pixel size of a photographed area of the camera unit by using an installation height, an installation angle, a view angle, and a resolution of the camera unit; an analyzer configured to analyze the number of pixels of the naked molten steel area contained in the molten steel surface image; a second calculator configured to calculate the size, which has a two-dimensional value, of the naked molten steel by multiplying the pixel size and the number of pixels; and a flow rate controller configured to obtain a diameter of a circle having the same size as the size, which has a two-dimensional value, of the naked molten steel to determine the obtained diameter as a converted size (D eq) having a one-dimensional value by using mathematical equation 4, and adjust a flow rate of a gas (g) supplied to the nozzle unit according to the converted value (D eq), D eq = sqrt the size of the naked molten steel × 4 / π, wherein sqrt represents square root, and D eq represents the converted size. a container unit having an open upper portion and an inner space in which a melt is refined; a nozzle unit installed on the container unit to blow a gas (g); a camera unit installed above the container unit to photograph a molten steel surface of the melt; and a control unit configured to calculate a size of naked molten steel on the molten steel surface by using a molten steel surface image obtained from the camera unit and installation information and performance information of the camera unit, wherein the installation information comprises an installation height and an installation angle of the camera unit, and the performance information comprises a view angle and a resolution of the camera unit, wherein the molten steel surface image is a single viewpoint molten steel surface image, wherein the control unit comprises: a deriver configured to derive the installation height with respect to the molten steel surface; a first calculator configured to calculate a pixel size of a photographed area of the camera unit by using an installation height, an installation angle, a view angle, and a resolution of the camera unit; an analyzer configured to analyze the number of pixels of the naked molten steel area contained in the molten steel surface image; a second calculator configured to calculate the size, which has a two-dimensional value, of the naked molten steel by multiplying the pixel size and the number of pixels; and a flow rate controller configured to obtain a diameter of a circle having the same size as the size, which has a two-dimensional value, of the naked molten steel to determine the obtained diameter as a converted size (D eq) having a one-dimensional value by using mathematical equation 4, and adjust a flow rate of a gas (g) supplied to the nozzle unit according to the converted value (D eq), D eq = sqrt the size of the naked molten steel × 4 / π, wherein sqrt represents square root, and D eq represents the converted size. a deriver configured to derive the installation height with respect to the molten steel surface; a first calculator configured to calculate a pixel size of a photographed area of the camera unit by using an installation height, an installation angle, a view angle, and a resolution of the camera unit; an analyzer configured to analyze the number of pixels of the naked molten steel area contained in the molten steel surface image; a second calculator configured to calculate the size, which has a two-dimensional value, of the naked molten steel by multiplying the pixel size and the number of pixels; and a flow rate controller configured to obtain a diameter of a circle having the same size as the size, which has a two-dimensional value, of the naked molten steel to determine the obtained diameter as a converted size (D eq) having a one-dimensional value by using mathematical equation 4, and adjust a flow rate of a gas (g) supplied to the nozzle unit according to the converted value (D eq), D eq = sqrt the size of the naked molten steel × 4 / π, wherein sqrt represents square root, and D eq represents the converted size.