  We construct two kinds of model exhibiting Higgs mechanism for gravitons in
potentials of scalar fields. One class of the model is based on a potential
which is a generic function of the induced internal metric $H^{AB}$, and the
other involves a potential which is a generic function of the usual metric
tensor $g_{\mu\nu}$ and the induced curved metric $Y_{\mu\nu}$. In the both
models, we derive conditions on the scalar potential in such a way that
gravitons acquire mass in a flat Minkowski space-time without non-unitary
propagating modes in the process of spontaneous symmetry breaking of
diffeomorphisms through the condensation of scalar fields. We solve the
conditions and find a general solution for the potential. As an interesting
specific solution, we present a simple potential for which the Higgs mechanism
for gravitons holds in any value of cosmological constant.
