  We study the baryonic three-quark (3Q) potential and its Abelian projection
in terms of the dual-superconductor picture in SU(3) quenched lattice QCD. The
non-Abelian SU(3) gauge theory is projected onto Abelian U(1)$^2$ gauge theory
in the maximal Abelian gauge. We investigate the 3Q potential and its Abelian
part for more than 300 different patterns of static 3Q systems in total at
$\beta=5.8$ on $16^332$ and at $\beta=6.0$ on $20^332$ with 1000-2000 gauge
configurations. For all the distances, both the 3Q potential and Abelian part
are found to be well described by the Y ansatz, i.e., two-body Coulomb term
plus three-body Y-type linear term $\sigma_{3\mathrm{Q}} L_{\mathrm{min}}$,
where $L_{\mathrm{min}}$ is the minimum flux-tube length connecting the three
quarks. We find equivalence between the three-body string tension
$\sigma_{3\mathrm{Q}}$ and its Abelian part $\sigma_{3\mathrm{Q}}^{\rm Abel}$
with an accuracy within a few percent deviation, i.e., $\sigma_{3\mathrm{Q}}
\simeq \sigma_{3\mathrm{Q}}^{\rm Abel}$, which means Abelian dominance of the
quark-confining force in 3Q systems.
