Water Problem, which is represented by the flooding and the drying in PEMFC, is one of the critical issues relating to the recent trend of high current density operation of it. For spreading the practical use of PEMFC, we must grasp this problem exactly and resolve it Two-phase flow numerical simulation is useful for this purpose. In this study, we numerically analyzed a unit-PEMFC two-dimensionally considering the two-phase flow based on the multiphase mixture model developed by Cheng and Wang, adding the authors' equivalent electric circuit. We simulated not only steady state but also unsteady state. A slightly abrupt change in current density distribution appeared on the point where the interface between the one- and the two-phase zone in GDL was appeared. The distribution of water saturation after cell operation start changed with time passed: the liquid water tend to focus on the GDL after once it spread in both GDL and flow channel.