A film forming apparatus includes a chamber having a processing space, a stage provided in the processing space and having a substrate placed thereon, a diffusion tube connected to the chamber so that a diffusion space communicating with the processing space is provided right above the stage, and a gas supply tube extending from the outside of the diffusion tube into the diffusion space through a portion of the diffusion tube and having a gas supply orifice in a portion thereof inside of the diffusion space. The gas supply orifice is formed so as to eject a material gas in a direction away from the stage.