  We construct a potential obtained by one-pion exchange for the coupled
channel $\Sigma_c^\ast$$\bar{D}$-$\Sigma_c$$\bar{D}^\ast$, and solve the
coupled Schr\"{o}dinger equations to determine the binding energy. We find that
there exists one or two bound states with the binding energy of several MeV
below the threshold of $\Sigma_c^\ast$ and $\bar{D}$, dominantly made from a
$\Sigma_c^\ast$ baryon and a $\bar{D}$ meson, with the size of about $1.5$fm
for wide parameter region. We also study the pentaquark states including a $b$
quark and/or an anti-$b$ quark. We show that there exist pentaquarks including
$c\bar{b}$, $b\bar{c}$ and $b\bar{b}$, all of which lie at about $10$MeV below
the corresponding threshold and have size of about $1.5$fm.
