Specific examples of the water-soluble high-molecular compounds include water-soluble polymers such as polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, a polyalkylene oxide such as polyethylene oxide or polypropylene oxide, and a polyalkylene oxide derivative; natural water-soluble polymers such as a polysaccharide, starc