  We construct a model of the quintessence axion based on a gauged chiral
$U(1)$ symmetry and an additional flat fifth dimension. The required high
qualities are guaranteed by the brane separation. The observed cosmological
constant (i.e., the potential energy of the quintessence axion) is determined
by the size of the extra dimension and the axion decay constant $F_a$ is fixed
almost at $F_a\simeq10^{17}\,{\rm GeV}$, which is sufficiently large for the
stability of the axion field near the hilltop of its potential. Furthermore,
the movement of the axion can also easily explain the recently reported
isotropic cosmic birefringence of the cosmic microwave background photon.
