Disclosed herein is a method of sequentially and continuously determining the concentrations of carbon, hydrogen, and nitrogen in molten steel using a single apparatus. Disclosed also herein are a method and an apparatus for determining trace amounts of carbon in molten steel which are the specialized application of the principle used for the above-mentioned method.Said method comprises bubbling through molten steel a carrier gas selected according to any specific element to be determined in molten steel, recovering the carrier gas containing the specific element, circulating or passing the recovered carrier gas through a gas circulating circuit so that the concentration of the specific element in the carrier gas reaches an approximate or complete equilibrium with the concentration of the specific element in molten steel, determining the concentration of the specific element by the means to determine the concentration of one or more specific elements, (and in the case of determination of several elements) discharging the carrier gas from the gas circulating circuit and repeating said steps with a renewed carrier gas to determine the remaining elements to be determined.