  We perform the first studies of various inter-quark potentials in SU(3)$_{\rm
c}$ lattice QCD. From the accurate lattice calculation for more than 300
different patterns of three-quark (3Q) systems, we find that the static 3Q
potential $V_{\rm 3Q}$ is well described by Y-Ansatz, i.e., the Coulomb plus
Y-type linear potential. Quark confinement mechanism in baryons is also
investigated in maximally-Abelian projected QCD. We next study the multi-quark
potentials $V_{n{\rm Q}}$ ($n$=4,5) in SU(3)$_{\rm c}$ lattice QCD, and find
that they are well described by the one-gluon-exchange Coulomb plus multi-Y
type linear potential, which supports the flux-tube picture even for the
multi-quarks. Finally, we study the heavy-heavy-light quark (QQq) potential
both in lattice QCD and in a lattice-QCD-based quark model.
