A plasma processing apparatus includes a chamber, a mounting table for mounting thereon a target object in the chamber, a plasma source configured to introduce microwaves into the chamber through a ceiling wall of the chamber and generate a surface wave plasma in the chamber, a first gas introduction unit for introducing a first gas into the chamber from the ceiling wall, and a second gas introduction unit for introducing a second gas into the chamber from a location between the ceiling wall and the mounting table. The second gas introduction unit includes a ring-shaped member having a plurality of gas injection holes and provided at a predetermined height position between the ceiling wall and the mounting table, and a leg part which connects the ceiling wall and the ring-shaped member. The second gas is supplied to the ring-shaped member through the leg part.