A polyurethane elastomer is produced by mixing a hardener composition containing a polyamine, a long chain polyol having an average molecular weight of 300 to 4,000 and a catalyst with an isocyanate composition comprises a prepolymer having terminal isocyanate group and an average molecular weight of 500 to 5,000 and an organic diisocyanate monomer with or without a triisocyanate monomer and a ratio of isocyanate groups of said prepolymer to amino groups of said polyamine is in a range of 0.6:1 to 1.5:1 and a ratio of a total of isocyanate groups in said isocyanate composition to a sum of amino groups of said polyamine and hydroxyl group of said long chain polyol is in a range of 0.8:1 to 1.4:1.