This invention provides a hydrocarbon concentration measuring apparatus, which, even when the concentration and composition of hydrocarbons contained in an object gas to be measured vary, can measure the concentration of the hydrocarbons with good response and good accuracy, and a hydrocarbon measuring method. Light with a waveband including a common absorption region, which is absorbed by a single or a plurality of chemical species, is applied to the object gas by an infrared irradiation equipment (130). The light applied to the object gas is detected with a line sensor (160). The absorbance in the common absorption region of the object gas is computed with an analyzer (190) based on the detected light. The sum of concentrations of chemical species, which absorb light in the waveband in the common absorption region, in the single or plurality of chemical species contained in the object gas, is computed with the analyzer (190) based on the absorbance.