Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, the method comprising:

• supplying a first reactant to inside a processing chamber into which a substrate has been introduced;
• controlling, with a first valve, a flow of a first purge gas into a first storage and storing the first purge gas, of which flow has been controlled with the first valve, in the first storage for a given time period;
• supplying the first purge gas from the first storage to the inside of the processing chamber by opening a second valve between the first storage and the processing chamber after supplying the first reactant;
• supplying a second reactant to the inside of the processing chamber after supplying the first purge gas;
• and
• supplying an auxiliary purge gas to the inside of the processing chamber,
• wherein supplying the auxiliary purge gas is performed simultaneously with the supplying of the first reactant, the supplying of the first purge gas, and the supplying of the second reactant.