A pressure-loss adjusting-member installation tool having pressure-loss adjusting-member grippers that are configured to freely grip or release a pressure-loss adjusting member which is arranged at a position between a lower nozzle arranged at one end of a fuel assembly having a relatively small pressure-loss when a primary coolant flows and a lower core support plate, and which can cause the primary coolant to pass therethrough in a state with a pressure-loss being increased more than that of when the primary coolant passes through only core support plate flow holes formed on the lower core support plate; and a holding unit that holds the pressure-loss adjusting-member grippers in a same positional relationship as a relative positional relationship between the fuel assemblies arranged in plural on the lower core support plate.