A shower plate of a processing gas supply unit disposed in a processing chamber of a substrate processing apparatus to supply a processing gas into a processing space in the processing chamber. The shower plate is interposed between a processing gas introduction space formed in the processing gas supply unit for introduction of the processing gas and the processing space. The shower plate includes processing gas supply passageways which allow the processing gas introduction space to communicate with the processing space. The processing gas supply passageways include gas holes formed toward the processing gas introduction space and gas grooves formed toward the processing space, the gas holes and gas grooves communicating with each other. A total flow path cross sectional area of all the gas grooves is larger than a total flow path cross sectional area of all the gas holes.