According to one aspect of the technique, there is provided a method of manufacturing a semiconductor device, including checking a leak from a process furnace before a substrate is processed. The checking includes: (a) measuring, by a partial pressure sensor provided at an exhaust pipe, an oxygen partial pressure value of a residual oxygen after the process furnace is vacuum-exhausted; (b) comparing the oxygen partial pressure value measured by the partial pressure sensor with a threshold value; and (c) when the oxygen partial pressure value is higher than the threshold value in (b), performing at least one among: purging the process furnace and evacuating the process furnace.