  H-alpha emission from supernova remnants (SNRs) implies the existence of
neutral hydrogens in the ambient medium. In the precursor of an SNR shock
modified by cosmic rays (CRs), upstream plasmas are pushed by the CR pressure,
but neutral particles are not, so that the relative velocity appears and some
neutral particles become pickup ions by the charge exchange process in the
precursor. We investigate how the pickup ions generated in the precursor affect
the shock structure and the particle acceleration. If the CR pressure is larger
than 20% of the shock ram pressure, the compression of the subshock becomes
smaller than that without pickup ions because of the pressure of the pickup
ions. Moreover, even if the shock is modified by CRs, the total compression
ratio can be smaller than 4. In addition, the pickup ions play an important
role for the injection into the particle acceleration. If the shock is a
quasi-perpendicular shock and if the the multiply reflected ion acceleration
occurs, the CR spectrum can be harder than that of the test particle diffusive
shock acceleration below GeV.
