There is provided a substrate processing apparatus including: a chamber in which a target substrate is accommodated; a first gas supply part configured to supply a gas containing a first monomer, and a gas containing a second monomer, which forms a polymer through a polymerization reaction with the first monomer, into the chamber so as to form a film of the polymer on the target substrate; an exhaust device configured to exhaust a gas inside the chamber; a first exhaust pipe configured to connect the chamber and the exhaust device; and an energy supply device configured to supply an energy with respect to a gas flowing through the first exhaust pipe so as to cause an unreacted component of at least one of the first monomer and the second monomer contained in the gas exhausted from the chamber to be reduced in a molecular weight.