The separation capability of the charged particles is one of the most important requirements for direct energy converters (DEC) of D-3He fusion reactors. Yasaka, one of the authors, has demonstrated the principle of the Cusp DEC on a small-scale experimental device. Analyses of the device with a two-dimensional approximation and comparison with the experimental results give the following results. (1) The input power of plasma beam is estimated as P = 2W × E1.5, compared with the experimental results, where E is the ion energy and normalized with 0.1keV. (2) The current at point cusp tends to saturate as the ion energy increases as the experimental results show. (3) Ion current at point cusp depends on the shape of the magnetic field more strongly than its strength.