  We propose a microscopical theory of superconductivity in CuO$_2$ layer
within the effective two-band Hubbard model in the strong correlation limit. By
applying a projection technique for the matrix Green function in terms of the
Hubbard operators, the Dyson equation is derived. It is proved that in the
mean-field approximation d-wave superconducting pairing mediated by the
conventional exchange interaction occurs. Allowing for the self-energy
corrections due to kinematic interaction, a spin-fluctuation d-wave pairing is
also obtained. $T\sb{c}$ dependence on the hole concentration and $\bf
k$-dependence of the gap function are derived. The results show that the
exchange interaction (which stems from the interband hopping) prevails over the
kinematic interaction (which stems from the intraband hopping).
