To prevent frosting in a supplying pipeline by a method wherein cooling air, supplied to cooling instruments, is manufactured by heat exchange between cooling liquid, consisting of liquid agent having moisture absorbing property, and recovering air.

In a machine room M, isolated from a shop S, a refrigerating cycle 2 for daytime cooling of a showcase 1, a cold storage tank 4, retaining cold heat of a first brine, a freezing cycle 5 for nighttime cooling, a cold air generating chamber 9, generating cooling air by effecting heat exchange between first brine as well as sprayed cooling liquid and surrounding medium to be cooled, and a moisture removing device 10 for cooling liquid, are arranged. In the cold air generating chamber 9, a heat exchanger or a cooling fin coil 6, a cooling liquid spray nozzle 7 nd a storage tank 8 are arranged. According to this method, the cooling air, manufactured in the cold air generating chamber, is dehumidified at all times whereby the air is dried. On the other hand, the cooling liquid adheres to the outer peripheral surface of the cooling fin coil and the like, arranged in the cold air generating chamber, whereby frosting to the cooling fin coil and the like can be prevented and a defrosting device itself becomes unnecessary.