To reduce the amount of standard liquid used for calibration and still facilitate the handing of it in calibration.

An operation control means 20 performs a normal TOC(total organic carbon) measurement by turning off all electromagnetic valves (a), (b), (c), and (d) and hence causing a combustion gas from a combustion pipe to flow to a drain from the electromagnetic valve (b) via an infrared gas analyzer 11. In the case of a calibration mode, by turning on the electromagnetic valves (a), (b), and (d) and turning off the electromagnetic valve (c), a path between the combustion pipe and the infrared gas analyzer 11 is broken, at the same time the infrared gas analyzer 11 and a trap 12 for adsorbing CO2 are connected, and further the trap 12 for adsorbing CO2 and the infrared gas analyzer 11 are connected via a bypass path 13a. By humidifying a temperature controller 12a in this state, CO2 with a known quantity being trapped by the trap 12 for adsorbing CO2 is eliminated and a calibration curve is constituted by a detection value which is successively detected by the infrared gas analyzer 11. The CO2 with a known quantity passing through the infrared gas analyzer is sucked by the trap 12 for adsorbing CO2 again.