To provide a method and apparatus for analyzing a compound sample, increasing the speed of quantitative analysis by at least four times than conventionally.

A single continuous segment fluid flow 100 is constituted of a plurality of segments. The segment includes four sample segments A-D divided by a segment S through which only a solvent flows. The sample segments A-D are selectively connected to a small spectrometer 40 at each prescribed time by a temporally controlled flow dividing valve 10. The mass spectrometer 10 conducts analysis of a sample, by relating the connection of the sample segments A-D to the corresponding sample compound.