  We study the superconductivity in the three-dimensional multiband d-p model,
in which a Cu$_2$O$_3$-ladder layer and a CuO$_2$-chain layer are alternately
stacked, as a model of the superconducting spin-chain ladder cuprate.
$p_z$-Wave-like triplet superconductivity is found to be the most stable, and
its dependence on interlayer coupling can explain the superconducting
transition temperature dependence on pressure in real superconducting
spin-chain ladder cuprates. The superconductivity may be enhanced if hole
transfer from the chain layer to the ladder layer can be promoted beyond the
typical transfer rate.
