Nitrile group-containing copolymer rubber, the crosslinkable rubber composition and crosslinked rubber product

alpha, containing β- ethylenically unsaturated nitrile monomer units in a proportion of 10 to 60 wt%, a nitrile group-containing copolymer rubber, wherein the weight average inertial radius is in the range of 10~100nm provide. According to the present invention, excellent workability, and can provide a nitrile group-containing copolymer rubber can provide excellent rubber cross-linked product in normal physical properties.