A film forming apparatus and a film forming method for suppressing a drop in the film forming speed caused by-product gas are provided. A film forming apparatus for forming a film on a wafer includes a chamber in which the wafer is located; a gas introducing member configured to introduce raw material gas into the chamber, in which the raw material gas turning into by-product gas and a substance which adheres to the surface of the wafer by reacting at a surface of the wafer; and a reverse reaction member configured to generate the raw material gas by causing the by-product gas to react in the chamber.