To prevent the penetration of rainwater and dust from a clearance generated between a seat plate and a ground surface, etc., when an entrance for a building is closed by a shutter.

This seat plate cover 6 is molded integrally of an elastic body such as a rubber in approximately the same length as a seat plate. The seat plate cover 6 contains a seat-plate cover body 10 covering the seat plate and tongue pieces 11a, 11b formed to a lower section in the longitudinal direction. The tongue pieces 11a, 11b are brought to the state, in which the tongue pieces are projected from the underside of the seat-plate cover body 10 approximately horizontally in both front and rear directions respectively.