  The Robnik billiard is investigated in detail both classically and quantally
in the transition range from integrable to almost chaotic system. We find out
that a remarkable correspondence between characteristic features of classical
dynamics, especially topological structure of integrable regions in the
Poincar\'{e} surface of section, and the statistics of energy level spacings
appears with a system parameter $\lambda$ being varied. It is shown that the
variance of the level spacing distribution changes its behavior at every
particular values of $\lambda$ in such a way that classical dynamics changes
its topological structure in the Poincar\'{e} surface of section, while the
skewness and the excess of the level spacings seem to be closely relevant to
the interface structure between integrable region and chaotic sea rather than
inner structure of intergrable regoin.
