The first experiments of neutral beam (NB) injection into a field-reversed configuration (FRC) plasma have been performed at FIX (FRC Injection Experiment) device.1 The experimental results show that the configuration lifetime of a FRC have been expanded by about 200% compared with no NB injection case. These results indicate that several hundred kilo watts of NB injection saves several mega watts of global energy losses. For understanding these experimental phenomena, some numerical calculations have been performed. Numerically calculated ionization degree vs. distance along beam injection axis and beam trajectories show that the injected beam ions form dense regions around minimum │B│. These formed hot beam ions walls would play a role in improving these confinements on the edge layer. Some previous theoretical studies pointed out the existence of electrostatic effects in the FRC edge plasma confinements.6, 7 Since only several kilo watts NB injection improves FRC confinement, it seems that the injected hot beam ions encourage electrostatic effects on the edge layer.