  We study the quark-hadron phase transition by using a three flavor
Nambu-Jona-Lasinio model with the Polyakov loop at zero chemical potential,
extending our previous work with two flavor model. We show that the equation of
state at low temperatures is dominated by pions and kaons as collective modes
of quarks and anti-quarks. As temperature increases, mesonic collective modes
melt into the continuum of quark and anti-quark so that hadronic phase changes
continuously to the quark phase where quark excitations dominate pressure.
