  We derive a gauge-invariant low-energy effective model of the SU(2)
Yang-Mills theory. We find that the effective gluon propagator belongs to the
Gribov-Stingl type, irrespective of the gauge choice. In the maximally Abelian
gauge, especially, we demonstrate that the model exhibits both quark
confinement and gluon confinement: the Wilson loop average has area law and the
Schwinger function violates reflection positivity. Moreover, we give a formula
for the string tension calculable from the gluon propagator of the
gauge-invariant field strength and gives a good estimate for the string
tension. We discuss if quark confinement and gluon confinement are of the same
origin attributed to the gluon propagator in the deep infrared momentum region.
