  We investigate the properties of nuclear matter at the first-order phase
transitions (FOPT) such as liquid-gas phase transition, kaon condensation, and
hadron-quark phase transition. As a general feature of the FOPT of matter
consisting of many species of charged particles, there appears a mixed phases
with regular structures called "pasta" due to the balance of the Coulomb
repulsion and the surface tension between two phases. The equation of state
(EOS) of mixed phase is different from those obtained by a bulk application of
Gibbs conditions or by the Maxwell construction due to the effects of the
non-uniform structure. We show that the charge screening and strong surface
tension make the EOS close to that of the Maxwell construction.
