There are provided a method of evaluating a quality of foods and drinks and an indicator therefor in which the quality of the foods and drinks, particularly the lowering of freshness, i.e. an amount of microorganism proliferated in the foods and drinks can be detected simply and accurately to judge the quality. That is, an aerogen consisting of at least one of yeast, mold and bacteria is sealed together with a fermentation substrate in a closed transparent vessel or transparent soft film bag of a synthetic resin and a quality of foods and drinks is judged by an amount of a gas generated through the formation of an acid generated in the vessel (bag), and there is used an indicator for evaluating thereof.