There is provided a gas supply apparatus 10 which does not necessitate installation of a pressure type flow controller for each processing reactor and which enables a compact construction of the flow controller. The gas supply apparatus 10 includes gas supply sources 11a, 11b, gas introduction pipes 13a, 13b, a main gas pipe 15, and branch pipes 21a, 21b. A pressure type flow controller 30 is provided for the main gas pipe 15 and the branch pipes 21a, 21b. The pressure type flow controller 30 includes a pressure detector 17 provided in the main gas pipe 15, and control valves 23a, 23b and orifices 22a, 22b, both provided in the branch pipes 21a, 21b. An arithmetic circuit 40 determines a flow rate Qc based on a detected pressure P1 from the pressure detector 17, and an arithmetic control circuit 58 controls the control valves 23a, 23b based on a set flow rate signal Qs from a flow rate setting circuit 52 and on the flow rate Qc from the arithmetic circuit 40.