To obtain a cooling system employing brine in which running cost of defrosting operation can be reduced and initial cost can also be reduced by making convenient the circuitry.

A brine cooling system 10 for cooling a plurality of showcases 13A, 13B, 13C,... comprises a brine chiller unit 14 for cooling brine, a primary circuit 11 having a primary pump 21 for circulating brine from the brine chiller unit, secondary circuits 12A, 12B, 12C,... having coolers 22 built in respective showcases, a secondary supply path 23 for supplying brine from the primary circuit to the cooler and a secondary return path 24 for returning brine from the cooler to the primary circuit, a secondary pump 30 arranged in the secondary return path of the secondary circuit, first solenoid valve 31 arranged in the secondary return path on the downstream side of the secondary pump, and a bypass circuit 29 branched from the secondary return path between the secondary pump and the first solenoid valve and connected with the secondary supply path while being provided with second solenoid valve 32 and a defrosting heat exchanger 33.