Seismic load induces a reverse cyclic load that alternately applies a tensile and a compressive load to a structure. For nuclear piping material, safety is assessed in terms of fracture toughness. However, test results using a quasi-static load can’t guarantee safety if there is a seismic load. In this paper, the fracture toughness of SA312 TP304 stainless steel, which is used as the safety injection pipe of a nuclear power plant, was estimated by using reverse cyclic loads with different ratios of tensile load to compressive load. The test results using a load ratio of -1 (compressive load / tensile load) show that fracture toughness decreases to approximately 10% against a load ratio of zero. These test results show that the reverse cyclic load must be considered in planning for the safety of nuclear power plants under seismic loads.