A computer readable storage medium storing a program for executing on a computer a method of cleaning a powdery source supply system in a substrate processing system including the powdery source supply system for supplying a powdery source and a film forming processing unit for performing a film forming process on a substrate by using the supplied powdery source, wherein the powdery source supply system has a chamber for accommodating the powdery source, a carrier gas supply unit for supplying a carrier gas into the chamber, an introduction line for connecting the chamber and the film forming processing unit and introducing a mixture of the carrier gas and the powdery source from the chamber to the film forming processing unit, a purge line branched from the introduction line and connected to a gas exhaust unit, and an opening/closing valve for opening and closing the introduction line between the film forming processing unit and a branch point from which the purge line emanates, and wherein the method includes a cleaning step in which the carrier gas supply unit supplies, when the opening/closing valve is closed and the interior of the purge line is evacuated prior to film forming process by the gas exhaust unit, the carrier gas so that viscous force acting on particles by the carrier gas is greater than viscous force acting on particles by the carrier gas in the film forming process.