In order to evaluate the effect of cusp magnetic field in the cylindrical Radially Convergent Beam Fusion (RCBF) device, four kinds of experimental setups were examined. The maximum Neutron Production Rate (NPR) of 7.4 x 109 n/s was obtained at -80 kV and 15 A. As a result of the theoretical evaluation of fusion regimes in the RCBF device, the NPR normalized by the cathode current and the gas pressure was compared between the setups. The experimental data showed that the normalized NPR is highly correlated with the gas pressure, and it was independent of the setups. As the gas pressure decreased, the normalized NPR was increased. Hence, the present study suggests that the effect of the cusp magnetic field is to achieve lower pressure operation which improves the normalized NPR. The numerical estimation became in agreement with the experimental result by introducing an adjusting factor which was highly correlated with the pressure. The difference of the pressure is expected to affect some factors, such as an effective cathode transparency.