Provided is a concentrated product production method using a membrane-concentration method and a freeze-concentration method that efficiently reduce (practically applicable) processing time (concentration time) as required in large-scale (commercial-scale) production. The concentrated product production method using a membrane-concentration method and a freeze-concentration method comprises: a membrane-concentration step in which a fluid to be treated is cooled, the solid-component concentration thereof is membrane-concentrated by at least 1.5 times, and a membrane-concentrated fluid to be treated is prepared； an ice crystal generation step in which the membrane-concentrated fluid to be treated is cooled, ice crystals of the membrane-concentrated fluid to be treated are generated in the membrane-concentrated fluid to be treated, and a mixed fluid is obtained, of ice crystals and concentrated fluid to be treated being membrane-concentrated fluid to be treated further concentrated as a result of the ice crystals being generated； and an ice crystal separation step in which the mixed fluid is separated into concentrated fluid to be treated and ice crystals, and the concentrated fluid to be treated is retrieved.
