A plasma etching device comprising: a chamber including a tubular body portion (5, 6), a top plate to close an upper portion of the body portion (5, 6), and a bottom plate to close a bottom portion of the body portion (5, 6) and having a plasma generation space set in an upper region in the body portion (5, 6) and a processing space set below the plasma generation space; an annular coil disposed outside a portion of the chamber corresponding to the plasma generation space; a platen disposed in the processing space in the chamber for placing a substrate to be processed thereon; a processing gas supply mechanism supplying a processing gas into the plasma generation space in the chamber; an exhaust mechanism exhausting at least gas inside the processing space in the chamber; a coil power supply mechanism supplying RF power to the coil; a platen power supply mechanism supplying RF power to the platen; a plasma density adjusting member comprising an annular member having an open upper end portion and an open lower end portion and having a shape with a diameter reduced toward the lower end portion, the upper end portion being fixed on an inner wall of the chamber between the plasma generation space and the platen, the plasma density adjusting member adjusting in-plane density of plasma generated in the plasma generation space and leading the plasma to the substrate placed on the platen, the plasma density adjustment member has a tapered shape with an upper end portion having a diameter larger than that of a lower end portion thereof; a cylindrical core member arranged to extend downward from a central portion of the top plate so that at least an lower end thereof is positioned below an upper end of the coil in a vertical direction; the body portion forming the plasma generation space being formed to have an inner diameter larger than an outer diameter of the substrate; and the plasma generation space being formed in a doughnut shape by the core member, characterized in that the core member has a lower end portion having a shape with a diameter reduced toward a lower end surface thereof, the lower end portion of the core member has a tapered shape having a diameter decreasing toward the lower end surface thereof, an angle (θ 1) between a horizontal plane and a generatrix of the tapered portion of the plasma density adjusting member is in a range of 52°-81°, and an angle (θ 2) between a horizontal plane and a generatrix of the tapered portion of the core member is equal to or larger than 80° but smaller than 90°. a chamber including a tubular body portion (5, 6), a top plate to close an upper portion of the body portion (5, 6), and a bottom plate to close a bottom portion of the body portion (5, 6) and having a plasma generation space set in an upper region in the body portion (5, 6) and a processing space set below the plasma generation space; an annular coil disposed outside a portion of the chamber corresponding to the plasma generation space; a platen disposed in the processing space in the chamber for placing a substrate to be processed thereon; a processing gas supply mechanism supplying a processing gas into the plasma generation space in the chamber; an exhaust mechanism exhausting at least gas inside the processing space in the chamber; a coil power supply mechanism supplying RF power to the coil; a platen power supply mechanism supplying RF power to the platen; a plasma density adjusting member comprising an annular member having an open upper end portion and an open lower end portion and having a shape with a diameter reduced toward the lower end portion, the upper end portion being fixed on an inner wall of the chamber between the plasma generation space and the platen, the plasma density adjusting member adjusting in-plane density of plasma generated in the plasma generation space and leading the plasma to the substrate placed on the platen, the plasma density adjustment member has a tapered shape with an upper end portion having a diameter larger than that of a lower end portion thereof; a cylindrical core member arranged to extend downward from a central portion of the top plate so that at least an lower end thereof is positioned below an upper end of the coil in a vertical direction; the body portion forming the plasma generation space being formed to have an inner diameter larger than an outer diameter of the substrate; and the plasma generation space being formed in a doughnut shape by the core member, characterized in that the core member has a lower end portion having a shape with a diameter reduced toward a lower end surface thereof, the lower end portion of the core member has a tapered shape having a diameter decreasing toward the lower end surface thereof, an angle (θ 1) between a horizontal plane and a generatrix of the tapered portion of the plasma density adjusting member is in a range of 52°-81°, and an angle (θ 2) between a horizontal plane and a generatrix of the tapered portion of the core member is equal to or larger than 80° but smaller than 90°.