The present invention provides an internal antenna type plasma processing device which is easily maintained and capable of producing stable plasma. The plasma processing device has a plurality of antenna units 20 provided in the top wall 111 of a vacuum chamber 11. Each of the antenna units 20 includes: a dielectric housing 21 provided to protrude into the vacuum chamber 11 from the top wall 111 of the vacuum chamber 11; a cover 22 having a second gas discharge port 25 for discharging the atmosphere in the housing to the outside of the vacuum chamber; and a radio-frequency antenna 23 formed by a conductor tube which is fixed to the cover 22 by way of a feedthrough 24 and has gas passage holes 232 in its tube walls. An inert gas is supplied into the tube of the radio-frequency antenna 23, and the inside of the housing 21 is filled with the inert gas provided through the gas passage holes 232. The inert gas is discharged to the outside of the vacuum chamber 11 through the second gas discharge port 25.