  We consider a superconductor-ferromagnet (S/F) structure and assume that
above the superconducting transition temperature $T_{c}$ the magnetic moment
exists only in F. {In a simple model of the ferromagnet (the exchange field is
of the ferromagnetic type for all energies)}we show by an explicit calculation
that below $T_{c}$ the magnetic moment may penetrate the superconductor. {In
this model} its direction in S is opposite {to the magnetization of free
electrons} in the ferromagnet. The magnetization spreads over a large distance
which is of the order of the superconducting coherence length $\xi_{S}$ and can
much exceed the ferromagnet film thickness. At the same time the magnetic
moment in the ferromagnet is reduced. This inverse proximity effect may explain
the reduction in magnetization observed in recent experiments and may lead to a
strong interaction between the ferromagnetic layers in F/S/F structures.
