To provide a substrate treating device capable of uniformly treating the surface of a substrate.

An RIE apparatus 100 is mainly composed a vacuum chamber 12, a substrate supporting mechanism consisting of a substrate supporting electrode 14, a counter electrode 16 and a gas introducing mechanism consisting of a gas supplying system 16. The substrate supporting electrode 14 is connected to a high-frequency power source 20 on the outside of the vacuum chamber 12. The counter electrode 16 and the gas supplying system 18 are connected via a gas introducing path 22. The counter electrode 16 is provided with a shower head 24. The substrate supplying surface 14a and the gas introducing surface 24a of the shower head 24 are disposed to face each other. The spacing between the gas introducing surface 24a of the shower head 24 and the substrate 10 supported by the substrate supplying surface 14a is about 50mm. The outside diameter of the gas introducing surface 24a, i.e., the outside diameter W2 of the shower head 24, is smaller than the outside diameter W1 of the substrate 10 supported on the substrate supporting surface 14a.