  The cosmological observation indicates that the effective equation of state
parameter $w_{eff}$ varies with $z$: It changes from $w_{eff}>-1$ to
$w_{eff}<-1$ at $z\sim 0.2$. We investigate under which condition it exhibits
such behaviors based on the five-dimensional braneworld scenario. It is
possible in the model with or without an energy exchange between the four
dimensional universe and the fifth dimension. However the curves of $w_{eff}$
are quite different between the two cases.
