Abstract: A substrate processing apparatus comprises: a reaction chamber for processing a substrate using a process gas; a pedestal provided in the reaction chamber and placing the substrate; and a shower head for introducing the process gas into the reaction chamber. The shower head includes a gas dispersion plate which is formed with a plurality of penetrating holes for diffusing the process gas and is provided to face the pedestal. The gas dispersion plate includes a central portion and a perimeter portion having a smaller thickness than the central portion, and the ones of the plurality of penetrating holes provided in the perimeter portion have a smaller length than the ones of the plurality of penetrating holes provided in the central portion.