  We study multi-quark (3Q,4Q,5Q) systems in lattice QCD. We perform the
detailed studies of multi-quark potentials in lattice QCD to clarify the
inter-quark interaction in multi-quark systems. We find that all the
multi-quark potentials are well described by the OGE Coulomb plus multi-Y-type
linear potential, i.e., the multi-Y Ansatz. For multi-quark systems, we observe
lattice QCD evidences of ``flip-flop'', i.e., flux-tube recombination. These
lattice QCD studies give an important bridge between elementary particle
physics and nuclear physics.
