PURPOSE: To measure the quantity of organic carbon highly accurately by making inorganic carbon material to be a gas, discharging the gas into an upper space in a storing tank, and guiding the gas together with an inactive gas into mixed liquid in a storing tank located at the neighboring upstream side through a second exhaust pipe.

CONSTITUTION: A degassing device 6 is provided. Mixed liquid of specimen water and acidic solution is stored in the device 6. The mixed liquid flows through a plurality of storing tanks 20A-20D sequentially along the arranged direction. Agitated gas jetting pats 24 are provided at the lower parts of the storing tanks 20A-20D. The mixed liquid is agitated in the parts 24, and the inactive gas is jetted from the parts 24. A first exhaust pipe 25D is provided at the most downstream side and exhaust the gas in the upper space of the storing tank 20D into an atmosphere. Second exhaust pipes 25A-25C guide the gas in the upper spaces of the storing tanks 20A-20C into the mixed liquid in the storing tanks at the neighboring downstream side. Said parts are provided. In this constitution, leaking of volatile organic carbon material which does not require degassing is prevented, and dissolution of carbon dioxide in ambient air into the liquid in the degassing device is prevented.