A device for measuring total organic carbon includes an organic substance oxidative decomposition section (4) for converting organic carbon contained in sample water into carbon dioxide, a carbon dioxide extraction section (6) for extracting carbon dioxide generated in the organic substance oxidative decomposition section (4) into measurement water, and a detection section for measuring the conductivity of the measurement water discharged from the carbon dioxide extraction section (6) to determine the amount of the extracted carbon dioxide. A syringe pump (12) is provided downstream of the detection section (11) in a measurement flow path (16) through which measurement water flows to pass through the carbon dioxide extraction section 6 and the detection section (11). The flow rate of measurement water during measurement of conductivity in the detection section (12) is controlled by suction into the syringe pump.