There is provided a technique that includes adjusting a pressure of each of a plurality of process chambers, by adjusting an opening degree of a pressure-adjusting valve included in a common gas exhaust pipe, which is connected to a plurality of process chamber exhaust pipes and is disposed to merge respective process chamber exhaust pipes on a downstream side of the plurality of process chamber exhaust pipes, to a predetermined opening degree and by exhausting an atmosphere of each of the process chambers from the plurality of process chamber exhaust pipes and the common gas exhaust pipe while supplying an inert gas to the plurality of process chambers; processing a substrate in each of the process chambers; and detecting a fluctuation of pressures in the process chamber exhaust pipes by measuring, by one or more pressure detectors, the pressures of the process chamber exhaust pipes.