  We study three subjects on quark confinement in hadrons 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 is
well described by Y-Ansatz, i.e., the Coulomb plus Y-type linear potential. We
also study the multi-quark (4Q, 5Q) potentials in lattice QCD, and find that
they are well described by the one-gluon-exchange (OGE) Coulomb plus
string-theoretical linear potential, which supports the {\it infrared string
picture} even for the multi-quarks. The second subject is a lattice-QCD
determination of the relevant gluonic momentum component for confinement. The
string tension (confining force) is found to be almost unchanged even after
cutting off the high-momentum gluon component above 1.5GeV in the Landau gauge.
In fact, {\it quark confinement originates from the low-momentum gluon below
about 1.5GeV.} Finally, we consider a possible gauge of QCD for the quark
potential model, by investigating "instantaneous inter-quark potential" in
generalized Landau gauge, which describes a continuous change from the Landau
gauge to the Coulomb gauge.
