  We present a model to investigate the formation and evolution of cluster
galaxies using cosmological N-body simulations. The N-body simulations are used
to make merging history trees of dark halos. Gas cooling, star formation,
supernova feedback and mergers of galaxies within dark halos are included by
using simple prescriptions taken from semi-analytic models of galaxy formation.
In this {\it Letter} we exam the merger-driven bulge formation model and
represent the morphology-density relation of cluster galaxies at z = 0. We find
that this morphological evolution model can explain the distribution of
elliptical galaxies in the clusters well and cannot reproduce the distribution
of S0 galaxies. This result suggests that the elliptical galaxies are mainly
formed by the major mergers, while, in the S0 formation, the processes other
than major mergers play important role.
