In order to clarify the electronic structure of the electron-doped superconducting material Nd_2–xM_xCuO₄, we have performed a first-principle band structure calculation for the matrix material Nd₂CuO₄. We find that doped electrons can be accommodated in both the Cu 4s and 4p _z conduction bands provided that the Cu 3dx²–y ² band splits into two bands, i.e., the upper and lower Hubbard bands by the strong correlation. Based on this electronic structure, we have calculated the Hall coefficient of the Nd system and have shown for the first time that the sign of the Hall coefficient is negative, coinciding with the experimental result in the low-concentration case. In the overdoped region above x=0.18, the dopant electrons occupy not only 4s and 4p _z bands but also the upper Hubbarddx ²–y ² so that the Hall coefficient changes its sign from negative to positive.