An object of the present invention is to provide a sensor that can quickly and easily detect primary aldosteronism with a higher accuracy. The present invention provides a method of quickly detecting aldosterone or renin in a sample with high sensitivity, using a multiphase polymer fine particles having at least on a surface thereof two or more polymer phases formed by aggregation of two or more polymers, respectively, wherein aldosterone or renin covalently binds to a first polymer phase, and wherein a second polymer phase has a labeling substance.