  The electronic state in layered cobalt oxides with hexagonal structure is
examined. We find that the electronic structure reflects the nature of the
Kagom\'e lattice hidden in the CoO_2 layer which consists of stacked triangular
lattices of oxygen ions and of cobalt ions. A fundamental model for the
electron system is proposed and the mechanism of the unique transport and
magnetic properties of the cobalt oxides are discussed in the light of the
model.
