  The ground-state three-quark (3Q) potential $V_{\rm 3Q}^{\rm g.s.}$ and the
excited-state 3Q potential $V_{\rm 3Q}^{\rm e.s.}$ are studied using SU(3)
lattice QCD at the quenched level. For more than 300 patterns of the 3Q
systems, the ground-state potential $V_{\rm 3Q}^{\rm g.s.}$ is investigated in
detail in lattice QCD with $12^3\times 24$ at $\beta=5.7$ and with $16^3\times
32$ at $\beta=5.8, 6.0$. As a result, the ground-state potential $V_{\rm
3Q}^{\rm g.s.}$ is found to be well described with Y-ansatz within the 1%-level
deviation. From the comparison with the Q-$\rm\bar Q$ potential, we find the
universality of the string tension as $\sigma_{\rm 3Q}\simeq\sigma_{\rm Q\bar
Q}$ and the one-gluon-exchange result as $A_{\rm 3Q}\simeq\frac12 A_{\rm Q\bar
Q}$. The excited-state potential $V_{\rm 3Q}^{\rm e.s.}$ is also studied in
lattice QCD with $16^3\times 32$ at $\beta=5.8$ for 24 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 1GeV in the typical hadronic scale, which is relatively large compared
with the excitation energy of the quark origin. This large gluonic excitation
energy justifies the great success of the simple quark model.
