PURPOSE: To enable detection of an amino acid component containing proline, cystine and the like in a short time with a simplified apparatus by setting a concentration of sodium hypochlorate (NaClO) that is oxidized with a primary amine to a specified range.

CONSTITUTION: First, 300×l of a 0.6 N sodium hydroxide liquid as reaction reagent and then, 300×l of 3ml/l NaClO (10% aqueous solution) are mixed with an automatic sampler 3 with a pretreating function. Here, when the concentration of NaClO is set in a range of 0.25-15ml/l referring to sensitivity of proline with a change therein, the proline is converted to primary amine. Then, a sample, boric acid, orthophthalic aldehyde in a bridge 35 solution and a 0.96 sulfuric acid/water for the protection of a column 4 are added to turn the final pH to acid. The mixture is separated with the column 4 controlling a mixing ratio between a 25mM phosphoric acid buffer and methylalcohol to detect 5 a fluorescence luminosity. This enable the detection of 18 components of amino acid including proline from cystine to lysine.