PURPOSE: To shorten the time required for extracting an IC component by introducing a sample added with non-oxidative protic acid on a boat into a thermal reaction section thereby accelerating reaction of inorganic carbon (IC) in the sample and the acid.

CONSTITUTION: A sample is mounted on a ceramic sample board 13 and introduced through the inlet of a sample introduction mechanism 14 into a reaction section 2 for measuring IC and then the inlet is closed. An inorganic acid is then added to the sample by means of an acid dispenser 18 and the boar 13 is moved 15 into an IC reaction tube 16 and the reaction of IC in the sample and the acid is accelerated in an IC furnace 17. Extraction of CO2 thus produced in gas phase is quickened and the extracted CO2 is introduced from a reaction section 1 for measuring total carbon (TC) through a cooling pipe 9 and a drain separator 10 to a nondispersive infrared spectrophotometer, along with carrier gas fed through the drain separator 10, in order to measure IC in the sample. This constitution shortens the time required for extraction of IC component in the sample and realizes quick and accurate measurement of total organic carbon TOC (=TC-IC).