An antifreeze protein is added to a hydrous material when the hydrous material contains water molecules and a substance other than water molecules, and freeze concentration of the substance should be inhibited; when the hydrous material contains a bioactive substance and inactivation of the bioactive substance should be inhibited; or when the hydrous material contains water molecules and a component other than the water molecules, and a frozen product or freeze-dried product in which the component is homogeneously dispersed should be produced.