PROBLEM TO BE SOLVED: To provide a technique for easily detecting catecholamines.SOLUTION: A method for detecting a detection target compound included in a sample solution is provided that comprises the steps of: mixing a metal particle formation agent with the sample solution to prepare a mixed solution; forming metal fine particles in the mixed solution; and optically analyzing the mixed solution. The target compound is represented by the following general formula, (where, Rrepresents a hydroxyl group; Rrepresents a straight chain or branch chain alkyl group having 1, 2 or 3 carbon atoms, a straight chain or branch chain alkenyl group having carbon 2 or 3 atoms, a hydroxyl group or hydrogen; the alkyl group and the alkenyl group may include one or more substituent groups; and the substituent group is selected from a group consisting of a hydroxyl group, an amino group, a carboxyl group and NH-CH.).
