Isocyanate composition, method for producing isocyanate polymer and isocyanate polymer

An isocyanate composition, comprising

• an isocyanate compound having an ethylenically unsaturated bond;
• and
• with respect to a total mass of the isocyanate compound, 1.0 to 1.0×104 ppm by mass of a compound different from the isocyanate compound and having at least one unsaturated bond other than an unsaturated bond constituting an aromatic ring, or
• with respect to a total mass of the isocyanate compound, 1.0 to 2.0×104 ppm by mass of an inert compound not having a carbon-carbon unsaturated bond other than an unsaturated bond constituting an aromatic ring, which is at least one selected from the group consisting of a hydrocarbon compound, an ether compound, a sulfide compound, a halogenated hydrocarbon compound, a silicon-containing hydrocarbon compound, a silicon-containing ether compound and a silicon-containing sulfide compound with respect to a total mass of the isocyanate compound, and/or 1.0 to 1.0×102 ppm by mass of a sulfuric acid and/or a sulfuric ester, and/or 1.0 to 1.0×102 ppm by mass of a phosphoric acid, and/or a phosphoric ester.