  For more than 300 different patterns of the 3Q systems, the ground-state 3Q
potential $V_{\rm 3Q}^{\rm g.s.}$ is investigated using SU(3) lattice QCD with
$12^3\times 24$ at $\beta=5.7$ and $16^3\times 32$ at $\beta=5.8, 6.0$ at the
quenched level. As a result of the detailed analyses, we find that the
ground-state potential $V_{\rm 3Q}^{\rm g.s.}$ is well described with so-called
Y-ansatz as $V_{\rm 3Q}=-A_{\rm 3Q}\sum_{i<j}\frac1{|{\bf r}_i-{\bf r}_j|}
+\sigma_{\rm 3Q} L_{\rm min}+C_{\rm 3Q}$, with the accuracy better than 1%.
Here, $L_{\rm min}$ denotes the minimal value of total flux-tube length. We
also studythe excited-state potential $V_{\rm 3Q}^{\rm e.s.}$ using lattice QCD
with $16^3\times 32$ at $\beta=5.8, 6.0$ for more than 100 patterns of the 3Q
systems. The energy gap between $V_{\rm 3Q}^{\rm g.s.}$ and $V_{\rm 3Q}^{\rm
e.s.}$, which physically means the gluonic excitation energy, is found to be
about 1 GeV in the typical hadronic scale. Finally, we suggest a possible
scenario which connects the success of the quark model to QCD.
