To provide a new leptospiral protein, to provide a gene encoding the same, to provide a new medicament having infection preventive action against leptospiral disease, and to provide a diagnostic kit for the leptospiral disease.

This leptospiral protein comprises a leptospiral protein LigA-m or a leptospiral protein LigB-m. The gene encodes the protein. The medicament contains the leptospiral protein LigA-m or LigB-m as an active ingredient and has the infection preventive action against the leptospiral disease. The diagnostic kit for the leptospiral disease contains the protein.