A gas supply system is provided. The system includes a plurality of component gas supply pipes, a plurality of flow rate control mechanisms for controlling flow rates of the component gases flowing in the component gas supply pipes, and a material gas supply pipe connected with downstream ends of the component gas supply pipes, and connected with one of the gas supply ports at a downstream. The flow rate control mechanism includes flow rate control valves, individual pressure sensors, and fluid resistance elements provided to the component gas supply pipes in this order from upstream, respectively, a common pressure sensor, and controllers for calculating the flow rates of the gases flowing in the component gas supply and controlling the flow rate control valves of the corresponding component gas supply pipes so that the calculated component gas flow rate approaches a predetermined gas flow rate, respectively.