PURPOSE: In dehydrating foods by the use of a substance having high osmotic pressure, to make it possible to use the substance having high osmotic repeatedly and to dehydrate foods efficiently and hygienically, by sterilizing the substance having high osmotic pressure to prevent multiplication of bacteria.

CONSTITUTION: When a substance having high osmotic pressure such as edible saccharide, mannan, sodium polyacrylate, propylene glycol, etc., is used as a dehydrating agent, the dehydrating agent is brought into contact with a food packaged with a water permeable semipermeable membrane through the water permeable semipermeable membrane, water in the food is permeated through the water permeable semipermeable membrane, absorbed in the substance having high osmotic pressure and the food is dehydrated, in the case where water activity of the substance having high osmotic pressure becomes ≥0.75, the substance having high osmotic pressure is sterilized by ultraviolet light irradiation method, ozone treatment method, etc.