  In this paper the scalar-tensor theory of gravity is assumed to describe the
evolution of the universe and the gravitational scalar $\phi$ is ascribed to
play the role of inflaton. The theory is characterized by the specified
coupling function $\omega(\phi)$ and the cosmological function $\lambda(\phi)$.
The function $\lambda(\phi)$ is nearly constant for $0<\phi<0.1$ and
$\lambda(1)=0$. The functions $\lambda(\phi)$ and $\omega(\phi)$ provide a
double-well potential for the motion of $\phi(t)$. Inflation commences and ends
naturally by the dynamics of the scalar field. The energy density of matter
increases steadily during inflation. When the constant $\Gamma$ in the action
is determined by the present matter density, the temperature at the end of
inflation is of the order of $10^{14} GeV$ in no need of reheating.
Furthermore, the gravitational scalar is just the cold dark matter that men
seek for.
