  A reduction of the density of states near the Fermi energy in the normal
state (pseudogap) of high-temperature oxide superconductors is examined on the
basis of the two-dimensional tight-binding model with effective interactions
due to antiferromagnetic fluctuations. By using antiferromagnetic correlation
lengths which are phenomenologically assumed, the doping dependence of the
pseudogap is obtained. The superconducting transition temperature decreases and
eventually vanishes due to the pseudogap as the hole concentration is reduced.
