A film coating agent for a solid formulation includes a water-soluble cellulose derivative, swelling clay, a cationic surfactant, and a fatty acid, wherein mass ratio of the swelling clay to the water-soluble cellulose derivative is 2:8 to 8:2, and content of the cationic surfactant is not less than 0.5 equivalents and not more than 3.0 equivalents relative to a cation exchange equivalent of the swelling clay.
