Provided is a method for measuring a color change of an oxidation-reduction indicator, which method is applicable to measurement of the cariogenic bacterial count and the like. A color change of an oxidation-reduction indicator is measured by a method for measuring a color change of an oxidation-reduction indicator, the method comprising reacting a test reagent with a test sample and measuring a color change, wherein the test reagent contains an oxidation-reduction indicator, an oxidation-reduction promoter, and a halogen salt.