Abstract: The gas supply system of this invention is furnished with a cylinder apparatus having a pneumatic valve that supplies process gas to a process chamber, and a solenoid valve that opens or closes said pneumatic valve by supplying or stopping the flow of valve actuating gas to said pneumatic valve; and a gas supply control apparatus that controls the actuation of the solenoid valve. In addition, said gas supply control apparatus comprises a main controller that controls the actuation of said solenoid valve during normal operation, and a sub-controller that senses an abnormal state of said main controller and if an abnormality is sensed, controls the actuation of said solenoid valve instead of said main controller.