PURPOSE:To form the crystal of ice, having suitable configuration and arrangement for freeze drying process, in the frozen layer of a material to be dried without any complicated operation by freezing the thin ice film of cleaning water on a cooling surface prior to the forming of the frozen layer of the material to be dried. CONSTITUTION:Cleaning water is poured from a supplying pipe 10 into cylindrical bodies 1, surrounded by cooling surfaces (a), to a predetermined level. Subsequently, the cooling surface (a) is cooled to form a thin ice layer on the cooling surface (a) and, thereafter, water, not frozen yet, is discharged out of the supplying pipe 10. Then, a material to be dried, whose density is regulated, is poured from the supplying pipe 10 into a space surrounded by the ice film to cool the cooling surface (a) and freeze the material to be dried around the nuclear of ice of the ice film for forming the crystal of ice at a low temperature slightly lower than a freezing point whereat the water becomes overcooled condition and is not frozen normally. After the frozen layer is formed, the material to be dried, which is not frozen yet, is dropped and, thereafter, freeze drying is effected while controlling a sublimating surface temperature under a given condition automatically.
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