Provided is a production method for a concentrated product, using a freeze-concentration method having a high yield rate (low loss rate) that is practically applicable, as required in large-scale (commercial scale) production. The production method for concentrated product using the freeze-concentration method includes: an ice crystal generation step in which a fluid to be treated is cooled, ice crystals of the fluid are generated in the fluid, and a mixed fluid to be treated is formed wherein the mixed fluid to be treated is comprised of the ice crystals and a concentrated fluid produced from the fluid to be treated by generating the ice crystals in the fluid thereby the fluid is concentrated； and an ice crystal separation step in which the mixed fluid is separated into the concentrated fluid to be treated and the ice crystals, and the separated concentrated fluid be treated is retrieved.
