Three-dimensional Monte Carlo analyses were performed for the three-legged beam ports of the laser fusion reactor SENRI-I. The validity of two devices for attenuating neutron flux was examined, and it was shown that the fast neutron flux attenuation of 1.4 × 105 can be reached by adopting these two devices in combination. The effectiveness of variance reduction techniques was also examined. It was determined that path length stretching was useful when it was used for neutron groups above 1 MeV. Adopting adjoint flux-dependent Russian roulette weight cutoff also seemed useful.