A plasma processing apparatus includes a processing container in which a plasma processing is performed on a substrate to be processed, a holding stage which is disposed in the processing container and holds thereon the substrate to be processed, a dielectric plate which is provided at a location facing the holding stage and transmits a microwave into the processing container, and a reactive gas supply unit which supplies a reactive gas for plasma processing toward the central region of the substrate to be processed held by the holding stage. Here, the reactive gas supply unit includes an injector base, which is disposed at a location more recessed inside the dielectric plate than a wall surface of the dielectric plate facing the holding stage. A supply hole, which supplies a reactive gas for plasma processing into the processing container, is formed in the injector base.