  We investigate the core structure of radiatively cooling intracluster gas,
using a hydrodynamics code. We calculate evolution of model clusters of the
initial core radii 160--300 kpc until the initial central cooling time, and
analyze the resultant clusters using the double beta-model as done by
observational studies. It is found that the core-size distribution thus
obtained shows two peaks \sim 30--100 kpc and \sim 100--300 kpc and marginally
can reproduce the observed distribution which exhibits two distinct peaks
around \sim 50 kpc and \sim 200 kpc. This result may suggest radiative-cooling
origin for small cores, while cooling is yet insignificant in the clusters of
large cores. It should be noted that the small core peak is reproduced by
clusters that are still keeping quasi-hydrostatic balance before the initial
central cooling time has elapsed.
