A theoretical description of the current formation in a device "source-molecule-drain" (SMD) is carried out for a special type of molecules with strongly separated energy levels. Owing to charge molecule-electrodes hoppings, the vacant molecular levels are populated by the transferred electrons, so that a molecule is kinetically charged. The theoretical explanation of the current-voltage characteristics of a molecule (Bu-2 N phi V)(2) BuPy I-+(-) is carried out, and it is shown that the rectification effect appears due to the asymmetric voltage drop across the molecule, as well as asymmetric molecular charging.