To provide a gas analyzer which efficiently and precisely analyzes impurities at ppb to sub-ppb level in a high-purity gas by integrating gas switching devices into one for minimum gas retention.

A gas switching device 21 comprises an analyzer lead-in path 22 which guides the sample gas from a sample gas source 11 to an analyzer 12 through an analyzer lead-in valve 22V, a separator lead-in path 23 which, branching from a primary path of the analyzer lead-in valve 22V, guides the sample gas to a separator 13 through a separator lead-in valve 23V, and a separator lead-out path 24 which guides the gas drawn from the separator 13 to a secondary path of the analyzer lead-in valve 22V through a separator lead-out valve 24V. Here, when the analyzer lead-in valve 22V is opened or closed, the separator lead-in valve 23V and the separator lead-out valve 24V are interlocked to be closed or opened.