A rubber-reinforcing cord (12) of the present invention includes at least one strand. The strand includes at least one filament bundle and a coating provided to cover at least a portion of the surface of the filament bundle. The coating contains a polymer and cellulose nanofibers, and does not contain a resorcinol-formaldehyde condensate. The polymer contains at least one selected from a polyurethane and a rubber component. In the coating, the content of the cellulose nanofibers is 0.1 to 10 parts by mass with respect to 100 parts by mass of the polymer. The proportion of the coating in the rubber-reinforcing cord is 18 vol % or more.