The mechanism of recently discovered high Tc Y–Ba type copper oxide superconductors is proposed by the two conduction band model of heavier and lighter electrons, taking into account of the infrared divergent effect due to the Fermi surface of the lighter electrons. The interaction between two heavy electrons, via a screened Coulomb interaction between a heavier and a lighter electrons, turns out to be attractive when their relative momentum is the Fermi momentum, though modified largely by the on site and screened Coulomb interaction but slightly by the Ruderman-Kittel-Yosida type spin-spin interaction between them. Tc is estimated to be of the order of one hundred degree Kelvin, depending on the magnitudes of the two band widths.