A plasma generating device includes: a chamber which is equipped with a dielectric wall structure and into which sample gas to be measured flows; an RF supplying mechanism that generates plasma inside the chamber using an electric field and/or a magnetic field through the dielectric wall structure; and a floating potential supplying mechanism that includes a first electrode disposed along an inner surface of the chamber. The RF supplying mechanism may include an RF field forming unit disposed in a first direction with respect to the chamber and the first electrode may include an electrode disposed in a second direction with respect to the chamber.