  The cross section of the ${}^{16}{\rm O}(p,p'){}^{16}{\rm O}(0^-,T=1)$
scattering was measured at a bombarding energy of 295 MeV in the momentum
transfer range of $1.0 \mathrm{fm^{-1}}$ $\le$ $q_{\rm c.m.}$ $\le$ $2.1
\mathrm{fm^{-1}}$.
  The isovector $0^-$ state at $E_x$ = 12.8 MeV is clearly separated from its
neighboring states owing to the high energy resolution of about 30 keV.
  The cross section data were compared with distorted wave impulse
approximation (DWIA) calculations employing shell-model wave functions.
  The observed cross sections around $q_{\rm c.m.}$ $\simeq$ $1.7 {\rm
fm^{-1}}$ are significantly larger than predicted by these calculations,
suggesting pionic enhancement as a precursor of pion condensation in nuclei.
  The data are successfully reproduced by DWIA calculations using random phase
approximation response functions including the $\Delta$ isobar that predict
pionic enhancement.
