The present invention prevents drop in the function of a plasma processing device caused by reduction of a plasma generating chamber by reductive plasma that is generated from the introduced process gas, and extends the life of members which are in contact with reductive plasma, especially the plasma generating chamber member. The plasma processing device of this embodiment is a device for treating the surface of a processing subject S using radicals generated by exciting a process gas, wherein a plasma generating chamber member 6, having a internal plasma generating chamber 6a, is connected to a gas introduction tube 5 attached to the outside of the process chamber 1, and a gas regulator 7 is provided on the end of the plasma generating chamber member 6. The configuration is such that when the plasma generating chamber member 6 is reduced by the reductive plasma generated from the gas introduced from the gas regulator 7, a reoxidation gas will be introduced into the plasma generating chamber 6a in place of the reductive gas from the gas regulator 7.