Disclosed is a plasma processing apparatus that processes a processing target substrate using microwave plasma within a processing container. The plasma processing apparatus includes a placing table provided in the processing container, and configured to place the processing target substrate thereon; and an antenna provided above the placing table to face the placing table, and including a dielectric plate, the antenna being configured to radiate microwaves into the processing container through the dielectric plate to generate plasma of a processing gas supplied into the processing container. The dielectric plate includes a flat plate portion provided on a bottom surface of the antenna, and formed in a flat shape at least on a surface facing the placing table; and a rib formed on a surface of the flat plate portion that is opposite to the surface facing the placing table.