  For a coefficient free cluster algebra $\mathcal{A}$, we study the cluster
automorphism group $Aut(\mathcal{A})$ and the automorphism group
$Aut(E_{\mathcal{A}})$ of its exchange graph $E_{\mathcal{A}}$. We show that
these two groups are isomorphic with each other, if $\mathcal{A}$ is of finite
type excepting types of rank two and type $F_4$, or if $\mathcal{A}$ is of
skew-symmetric finite mutation type.
