  We study a one-dimensional SU(N) Hubbard model with an attractive on-site
interaction and $N>2$ at half-filling on the bipartite lattice using
density-matrix renormalization-group method and a perturbation theory. We find
that the ground state of the SU(N) Hubbard model is a charge density wave state
with two-fold degeneracy. All the excitations are found to be gapful, resulting
in an insulating ground state, on contrary to that in the SU(2) case. Moreover,
the charge gap is equal to the Cooperon gap, which behaves as $-2Nt^2/(N-1)U$
in the strong coupling regime. However, the spin gap $\Delta_{s}$ and the
quasiparticle gap $\Delta_{1}$ as well open exponentially in the weak coupling
region, while in the strong coupling region, they linearly depend on $U$ such
that $\Delta_{s}\sim -U(N-1)$ and $\Delta_{1}\sim -U(N-1)/2$.
