A method of manufacturing a semiconductor device, the method including supplying a first reactant to inside a processing chamber into which a substrate has been introduced; controlling a flow of a first purge gas and storing the first purge gas, of which flow has been controlled, in a first storage for a given time period; supplying the first purge gas from the first storage to the inside of the processing chamber after supplying the first reactant; and supplying a second reactant to the inside of the processing chamber after supplying the first purge gas.