A substrate processing apparatus that can reduce the number of parts. A first gas introduction hole through which the hydrogen fluoride gas is introduced into a GDP is formed in an upper lid. A second gas introduction hole through which hydrogen fluoride gas is introduced from a hydrogen fluoride gas source is formed in a processing vessel. When the upper lid engages the upper portion of the processing vessel, one end of the first gas introduction hole is joined with one end of the second gas introduction hole to form an introduction path through which the hydrogen fluoride gas is introduced into a chamber.