In the plasma generator 200, by applying a voltage between the electrodes 201 and 201 while introducing a gas for generating plasma G through the top opening, a number of streamer discharge S is generated in an opposing region 202. Here, the gas for generating plasma G is introduced from a gas introduction hole 223 through an orifice 225 of a jetting plate 224 into an opposing region 202, hence the gas for generating plasma G is accelerated by the orifice 225 to jet into the opposing region 202 at high speed. This jet causes turbulence in the gas for generating plasma G, which in turn causes the streamer discharge S to be diffused and dispersed in the opposing region 202. Then, the dispersed streamer discharge S generates plasma P substantially uniformly throughout the entire opposing region 202, and this plasma P is blown out from the bottom opening of the opposing region 202 into a processing space 205 as plasma jet, spraying onto an object to be treated H. Patent Document 1 discloses that adopting the above configuration makes it possible to generate uniform plasma. Meanwhile, an electrode layer is designed to be thick such that an electrode section holds a dielectric body to secure the overall strength. In such a case, the dielectric body is very susceptible to cracking due to a difference in linear expansion coefficient between dielectric material and metal constituting an electrode, which poses a problem from a viewpoint of a service life. Typically, the dielectric body is made of ceramic materials, and the electrode is made of metal. Using the dielectric body having a thin wall causes a mechanical strain to occur due to the difference in linear expansion between ceramics and metal. This mechanical strain results in damaging the thin ceramics. A method to address this drawback includes that the thickness of the ceramics increases to secure its strength. However, when the thickness of the dielectric body increases, the dielectric loss also increases, which poses a problem of sacrificing the efficiency of plasma generation.