  A pseudo-Goldstone boson for {\it quintessence} is known to require the decay
constant $F_q\sim M_P$ and the height of the potential $(0.003 {\rm eV})^4$,
and hence the pseudo-Goldstone boson mass of order $10^{-33}$ eV. The
model-dependent axion in some superstring models is suggested as a good
candidate for the quintessence. We realize this idea with a hidden-sector gauge
group $SU(3)_H\times U(1)_H$. The hidden-sector instanton contribution to the
quintessence potential is suppressed by the almost massless hidden-sector
quarks. The model-independent axion is the QCD axion required for the strong CP
solution.
