NOVELTY - The method involves recalculating synthetic flow volume correction coefficient of sample gas from component concentration before dilution of the gas (S2). A dilution ratio is recalculated (S3) from a flow volume indicated value. A difference of component concentration before dilution of the gas that carries out recalculation, and the concentration before dilution of the gas before the recalculation is calculated (S6). The concentration before dilution of the gas that carries out the recalculation is used (S9) when the difference is equal to a threshold value.    USE - Method for calculating an exact component concentration of sample gas e.g. nitrogen gas and argon gas, before dilution from the component concentration of the sample gas obtained from an internal combustion engine, fuel reforming system and a fuel cell.    ADVANTAGE - The method enables using the flow volume correction coefficient of the component of sample gas and the intrinsic flow volume correction coefficient of a mass flow meter such that component concentration before dilution of the sample gas obtained from the dilution ratio acquired from the measured value of the mass flow meter and the measured value of the mass flow meter and the dilution ratio in accordance with a repeated calculation method can be repeatedly corrected until a predetermined precision is acquired, thus calculating an exact component concentration of the sample gas can be carried out regardless of the dilution ratio of sample gas.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a sample gas component concentration calculation apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating a gas component concentration calculation method. '(Drawing includes non-English language text)'    Step for measuring after-dilution component concentration of sample gas (S1)    Step for recalculating synthetic flow volume correction coefficient of sample gas from component concentration before dilution of the gas (S2)    Step for recalculating dilution ratio from a flow volume indicated value (S3)    Step for calculating difference of component concentration before dilution of the gas that carries out recalculation, and concentration before dilution of the gas before recalculation (S6)    Step for using concentration before dilution of the gas that carries out the recalculation when difference is equal to a threshold value (S9)