  The gauged Peccei-Quinn (PQ) mechanism provides a simple prescription to
embed the global PQ symmetry into a gauged $U(1)$ symmetry. As it originates
from the gauged PQ symmetry, the global PQ symmetry can be protected from
explicit breaking by quantum gravitational effects once appropriate charge
assignment is given. In this paper, we identify the gauged PQ symmetry with the
${B-L}$ symmetry, which is obviously attractive as the ${B-L}$ gauge symmetry
is the most authentic extension of the Standard Model. As we will show, a
natural $B-L$ charge assignment can be found in a model motivated by the seesaw
mechanism in the $SU(5)$ Grand Unified Theory. As a notable feature of this
model, it does not require extra $SU(5)$ singlet matter fields other than the
right-handed neutrinos to cancel the self and the gravitational anomalies.
