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 a surface of the filament bundle. The coating includes a rubber component including at least one selected from the group consisting of carboxyl-modified nitrile rubber and carboxyl-modified hydrogenated nitrile rubber, an isocyanate compound, a bismaleimide compound, carbon black, and a rubber-modified epoxy resin. In the coating, the content of the isocyanate compound is 10 to 50 parts by mass, the content of the bismaleimide compound is 5 to 25 parts by mass, the content of the carbon black is 2 to 18 parts by mass, and the content of the rubber-modified epoxy resin is 5 to 30 parts by mass, with respect to 100 parts by mass of the rubber component.