To attach a nail decorating base board to a nail in a single operation, to decorate not only a part but also the whole of a nail surface, to prevent the imposition of a large burden on the nail when installed on the nail, and to prevent the nail decorating base board from easily falling off from the nail.

A locking part 12 curved downward and backward in a state of integrally continuing with a base board body part 11 is arranged on the tip of the plate-like base board body part 11 curved along a nail surface so as to be arranged along the nail surface. A rear end part of the locking part 12 is brought into pressure contact with a tip part under surface of a nail by elastic force when a tip part of the nail is fitted between the rear end part and the base board body part 11.