[en] The finite element method has been applied to solve accurately the multi-dimensional neutron diffusion equation on a modern computer. A new computer program FEM-BABEL has been developed by adopting the solution algorithm based on the Galerkin-type scheme. This three-dimensional program makes use of the combination of prism- and box-shaped elements to simulate reactor geometries efficiently. The successive over-relaxation method is adopted to solve the system equation and the inner iterations are accelerated using the coarse mesh rebalancing technique. Numerical calculations have demonstrated the present finite element method has advantages over the finite difference method for solving realistic three-dimensional problems in view of computing cost. (auth.)