In order to provide an absorbance analysis apparatus for DCR gas that can measure a concentration of a DCR gas by separating absorbance of the DCR gas alone even in a mixed gas consisting of the DCR gas and CO gas whose absorption spectrum overlaps each other, the absorbance analysis apparatus for DCR gas comprises a DCR filter 31 that is configured to transmit a light in a first wavenumber domain including an absorbance peak of the DCR gas, a CO filter 32 that is configured to transmit a light in a second wavenumber domain that is different from the first wavenumber domain, and a DCR gas volume calculator 4 that is configured to calculate volume of the DCR gas based on a first absorbance measured by the light transmitted through the DCR filter 31 and a second absorbance measured by the light transmitted through the CO filter 32.