Gas flow monitoring system

A gas flow monitoring system to be provided in a plurality of process gas lines each being arranged to supply gas from a process gas supply source to a predetermined process chamber via a flow control device, the system being configured to measure lowering or rising of gas pressure before and after the flow control device to monitor a flow rate of the flow control device, the system including:

• a first flow monitoring unit placed in a passage located upstream of the flow control device in an arbitrarily selected process gas line of the process gas lines;
• a second flow monitoring unit placed in a discharge passage branching from a passage located upstream of the process chamber;
• and
• a controller that constantly monitors a flow rate of the flow control device with the first flow monitoring unit and that, when the first flow monitoring unit verifies the flow rate by a predetermined number of times, commands the first and second flow monitoring units to simultaneously verify the flow rate and commands the first flow monitoring unit to correct, based on a flow-rate verification result of the second flow monitoring unit, a verification deviation amount defined by a difference between a flow rate calculated in the flow-rate verification performed by using the first flow monitoring unit and a flow rate set in the flow control device.