To improve processing quality by inhibiting the generation of a strong electric field and high-density plasma, near a contact point between a support part supporting a transmissive window and the transmissive window in a plasma processing apparatus utilizing a microwave. In a plasma processing apparatus that processes a wafer W in a process vessel 2 by plasma generated by the supply of a microwave, a transmissive window 20 has, in a center area of its lower surface, a hanging portion 21 made of the same material as a material of the transmissive window 20. Between an outer peripheral surface 21a of the hanging portion 21 and a sidewall inner surface 5a continuing from a support part 6, a gap d is formed, the gap d having a gap length of 0.5 to 10 mm, more preferably 0.5 to 5 mm. The generation of a strong electric field and plasma at the contact point C is inhibited and an amount of sputtered particles, radicals, or the like reaching the wafer W is also reduced.