The present invention includes a first flow path through which a sample gas flows, a first analyzer that is provided in the first flow path to measure total hydrocarbon concentration in the sample gas, a second flow path through which the sample gas flows, a non-methane non-ethane cutter that is provided in the second flow path to remove the hydrocarbon components other than the methane and the ethane in the sample gas, a second analyzer that is provided downstream of the non-methane non-ethane cutter in the second flow path to measure the total methane ethane concentration of the methane and the ethane in the sample gas, and a calculation part that calculates the concentration of the hydrocarbon components other than the methane and the ethane in the sample gas with use of the total hydrocarbon concentration by the first analyzer and the total methane ethane concentration by the second analyzer.