In a film forming apparatus according to the aerosol deposition method, the thickness of a structure being formed can be controlled accurately. The film forming apparatus includes an aerosol generating part in which raw material powder is to be provided, a compressed gas cylinder and a pressure regulating part for introducing a gas into the aerosol generating part to blow up the raw material powder thereby generating an aerosol, a substrate holder for holding a substrate on which a structure is to be formed, a nozzle for spraying the aerosol generated in the aerosol generating part toward the substrate, and a sensor to be used for obtaining an amount of primary particles that have contributed to film formation by impinging on the substrate or the structure formed thereon from among the raw material powder contained in the aerosol sprayed from the nozzle.