The present invention provide a method for detecting a test substance utilizing a color development caused by an enzyme reaction, or a color development caused by a specific interaction such as an antigen-antibody reaction and an enzyme reaction, the test substance being detected rapidly, sensitively and quantitatively without using a spectroscopic measurement device. The method for measuring a concentration of a test substance by the present invention comprises the steps of: generating a peroxide from the test substance; obtaining a polymerized substance by bringing an oxidoreductase for producing a polymerized substance and a substrate of the oxidoreductase for producing a polymerized substance into contact with the peroxide; and irradiating the polymerized substance with light to record a temporal variation information of an intensity of scattered light generated from an irradiation point.