To provide a rubber composition which is easily processed in the uncrosslinked state such as rolling and molding, without the viscosity rising, and a belt which has a very high hardness and high strengths after crosslinking.

In the belt comprising as a major component a hydrogenated nitrile rubber containing a metal salt of an unsaturated carboxylic acid, the hydrogenated nitrile rubber comprises the metal salt of the unsaturated carboxylic acid as a matrix rubber, 10-60 parts by mass of silica added to 100 parts by mass of the matrix rubber, and 5-20 parts by mass of triallylisocyanurate or triallycyanurate formulated as the co-crosslinker, and is crosslinked with an organic peroxide.