The most important issues to introduce FCVs into the market are downsizing and cost reduction of the fuel cell stacks and its system components. From one of them, simplifying the hydrogen supplying system is highly expected. With the aim of eliminating the hydrogen recirculation system, transient mass transport analysis which are the CFD analysis with compressive low Re number flow field and a time-series measurement with mass spectroscopes to investigate the gas distribution in the anode flow channel have been implemented. This paper presents the time-varying gas concentration distribution.