PURPOSE: To measure organocarbon by individual plural components being contained, by dividing a specimen corresponding to the characteristics of the evaporation and thermal decomposition of the organocarbon component of the specimen and burning the same to detect CO2.

CONSTITUTION: An organocarbon component contains a component (POC) purged only by carrier gas, a low b.p. component like ethanol and a high b.p. component like glycerine. A specimen is introduced into an evaporation tube 8 from an injection pipe 1 while carrier gas (purified air) is introduced into the evaporation tube 8 from a supply part 3 to be evaporated and subsequently burnt in a combustion pipe 13 to form CO2 which is, in turn, detected by a detector 15 to measure carbon. At this time, the carrier gas is allowed to pass at ambient temp. at first to evaporate the component POC which is, in turn, burnt at about 800°C to detect CO2. Next, the evaporation tube 8 is heated to about 150°C or to 800°C to respectively evaporate the low b.p. component or the high b.p. component which is then burn to detect CO2. Since the specimen components are divided, and evaporated and thermally decomposed to detect CO2, organocarbon can be measured not as total quantity but as respective quantities of a plurality of the components divided.