To safely store natural gas in gas storage facilities requiring a smaller installation area.

Gas storage facilities comprise a hydrator tank 30 which bleeds its vessel 31 for storing cold water therein of cold water and cools it to form ice grains to be circulated on the water surface in the vessel 31, and then feeds natural gas under the surface of the cold water including the ice grains to form hydrate (h) to be stored at the bottom of the vessel 31; and a separator 61 for separating the stored hydrate (h) lead thereto into natural gas and water.