There is provided technique including: forming film on substrate by performing cycle, predetermined number of times, including non-simultaneously performing: (a) supplying precursor gas and inert gas to the substrate; and (b) supplying reaction gas to the substrate, wherein in (a), at least one selected from the group of the precursor gas and the inert gas stored in first tank is supplied to the substrate, and at least one selected from the group of the precursor gas and the inert gas stored in second tank is supplied to the substrate, and concentration of the precursor gas in the first tank while at least one selected from the group of the precursor gas and the inert gas is stored in the first tank differs from that in the second tank while at least one selected from the group of the precursor gas and the inert gas is stored in the second tank.