A beam energy recovery system for future neutral beam injectors based on negative ions has been designed. Residual negative ions are recovered electrically, while residual positive ions are decelerated on a soft-landing beam dump. This design simplifies the beam energy recovery power supply system and reduces the heat flux on the beam dump. Residual ions are separated into negative and positive ions by the stray magnetic field from the Fusion Engineering Reactor (FER), the next Japanese tokamak reactor. Each ion beam is also guided to the collector electrode and the soft-landing beam dump by the stray magnetic field. In the 500-keV/20-MW injector designed for FER, the total power efficiency can be improved from 46 to 59% by recovering the negative ions.