A film forming apparatus includes a mounting table mounting a substrate thereon, a gas diffusion unit above the mounting table, gas dispersion units above the gas diffusion unit, and an evacuation unit to evacuate a processing chamber. The gas diffusion unit has gas injection holes for injecting a gas in a shower shape. Outermost gas injection holes are arranged outward of an outer circumference of the substrate when seen from the top. The gas dispersion units face the gas diffusion unit through a diffusion space therebetween. Each of the gas dispersion units has gas discharge holes formed along a circumferential direction thereof to disperse a gas horizontally into the diffusion space. The gas dispersion units include at least three first gas dispersion units along a first circle, and at least three second gas dispersion units along a second circle concentrically disposed at an outer side of the first circle.