PURPOSE: To achieve simultaneous separation and analysis of strongly and weakly held anion species, by holding a strongly held ion species with a low holding capacity column and a weakly held ion species with a high holding capacity column to set a mobile phase passage properly.

CONSTITUTION: Holding capacity of columns 4 and 5 is adjusted before a measurement so that analysis time of a strongly held anion species (So42- or the like) with a low holding capacity column 4 is equal to the analysis time of a weakly held anion species (Cl- or the like) with a high holding capacity column 5. Valves A and B are switches properly to run a mobile phase from a passage (a). A sample 3 is introduced into the column 4 via a passage (c) to hold a strong ion species. The remaining sample is introduced into the column 5 via a passage (e) to hold a weak ion species. Thereafter, the mobile phase is passed through the column 5 to separate the weak ion species and it runs to passages (d), (f) and (c) to separate the strong ion species passing through the column 4. In this manner, strong and weak ion species are detected with a detector 6, thereby enabling analysis of strongly and weakly held anion species at a close timing.