Abstract: An apparatus for analyzing oxygen, nitrogen and hydrogen which are contained in metals. The apparatus includes a graphite crucible which has a sample therein and which is heated to generate a gaseous mixture of CO, N.sub.2 and H.sub.2. An oxidizer is used to oxidize the CO and H.sub.2 into CO.sub.2 and H.sub.2 O, respectively. The apparatus further includes a thermal conductivity detecting means for detecting CO.sub.2, N.sub.2 and H.sub.2 O, coming from a first gas-chromatographic column which is used for separating H.sub.2 O from the CO.sub.2 and N.sub.2. A second gas-chromatographic column is used for separating CO.sub.2 from N.sub.2. A passage change valve is used for back-flushing the first column. Helium is preferably used as the carrier gas. The apparatus is simple and operates quickly because the three components, O, N and H, can be measured by using a single carrier gas He and a single sample and thus, only a single measurement operation is required.