A nuclear reactor upper structure with an earthquake-resistant reinforcement assembly, said earthquake-resistant reinforcement assembly comprising: a rod, a first end of which is hinge-coupled to the nuclear reactor upper structure; a coupling pin arranged at a second end of the rod, and extended to diametrically cross the rod; and a bracket adapted to be installed at a partition wall of a nuclear reactor containment building, and coupled to the second end of the rod, wherein the bracket comprises: a first member and a second member, wherein the coupling pin is formed at the second end of the rod, the first member and the second member are extended in parallel to face each other so that the first member and the second member form both lateral walls of a first groove so as to allow the second end of the rod to be placed between the first member and the second member; a second groove with a first surface adjacent to the nuclear reactor upper structure and a second surface facing the first surface is formed on the first member, and a third groove with a third surface adjacent to the nuclear reactor upper structure and a fourth surface facing the third surface is formed on the second member, wherein the second groove and the third groove are designed to be coupled to the coupling pin, and wherein the first surface, the second surface, the third surface and the fourth surface are formed to be inclined by 5 to 20 degrees toward a vertical surface of the nuclear reactor upper structure. a rod, a first end of which is hinge-coupled to the nuclear reactor upper structure; a coupling pin arranged at a second end of the rod, and extended to diametrically cross the rod; and a bracket adapted to be installed at a partition wall of a nuclear reactor containment building, and coupled to the second end of the rod, wherein the bracket comprises: a first member and a second member, wherein the coupling pin is formed at the second end of the rod, the first member and the second member are extended in parallel to face each other so that the first member and the second member form both lateral walls of a first groove so as to allow the second end of the rod to be placed between the first member and the second member; a second groove with a first surface adjacent to the nuclear reactor upper structure and a second surface facing the first surface is formed on the first member, and a third groove with a third surface adjacent to the nuclear reactor upper structure and a fourth surface facing the third surface is formed on the second member, wherein the second groove and the third groove are designed to be coupled to the coupling pin, and wherein the first surface, the second surface, the third surface and the fourth surface are formed to be inclined by 5 to 20 degrees toward a vertical surface of the nuclear reactor upper structure. a first member and a second member, wherein the coupling pin is formed at the second end of the rod, the first member and the second member are extended in parallel to face each other so that the first member and the second member form both lateral walls of a first groove so as to allow the second end of the rod to be placed between the first member and the second member; a second groove with a first surface adjacent to the nuclear reactor upper structure and a second surface facing the first surface is formed on the first member, and a third groove with a third surface adjacent to the nuclear reactor upper structure and a fourth surface facing the third surface is formed on the second member, wherein the second groove and the third groove are designed to be coupled to the coupling pin, and wherein the first surface, the second surface, the third surface and the fourth surface are formed to be inclined by 5 to 20 degrees toward a vertical surface of the nuclear reactor upper structure.