A filament driven multi-cusp negative ion source has been developed for proton cyclotron applications. In this study, numerical analysis of the H- volume production in the negative ion source has been conducted by the KEIOMARC code and zero dimensional rate equations. The code calculate the Electron Energy Distribution Function (EEDF) in multi-cusp arc discharge sources from the following main input parameters: 1) 3D geometry of the source chamber and filaments, 2) 3D magnetic configuration, 3) arc voltage, 4) arc current and 5) gas pressure. Using the EEDF, we can also estimate the resultant amount of the H- volume production by the 0D rate equations. In this paper, we focus on the dependency of the H- production on the filter magnetic field and the arc-discharge voltage. It is shown that KEIOMARC code reproduces the magnetic filter effect, i.e., the electron temperature and density are reduced across the filter region. Also, the 0D analysis shows that the amount of H- production increases with the arc-voltage, but is gradually saturated in the high voltage region (Varc>150V). The mechanism which leads to the saturation is possibly explained by the saturation of the electron density in such a high voltage regime.