PURPOSE: To determine a small amount of carbon constituent in a metal sample simply and rapidly by isolating surface-contaminating carbon constituent.

CONSTITUTION: A metal sample 4 is first heated in an inactive gas flow, a contaminating carbon constituent remaining on the surface of the sample is eliminated, the inactive gas is switched to oxygen gas while successively heating it, and the sample 4 is subjected to an oxidation combustion, thus forming the carbon constituent in the sample to be carbon dioxide. A carbon content in the sample where the amount of sample surface-contaminating carbon is subtracted from the generated carbon dioxide gas concentration, is obtained accurately, simply, and rapidly.