PROBLEM TO BE SOLVED: To provide a plasma generator capable of processing water to be processed with higher reaction efficiency than that of a conventional atmospheric plasma generator or underwater plasma generator, a nitrogen source manufacturing device, a nutrient solution supply device, a raising system, a plant cultivation system, a method for manufacturing a nitrogen source and a method for reducing carbon dioxide.SOLUTION: The present invention relates to a plasma generator including a cathode 1 and an anode 2. The cathode 1 and the anode 2 are disposed while interposing a clearance where plasma is generated by applying a voltage between both the cathode and the anode. Each of the cathode 1 and the anode 2 includes an electrode and an insulation material covering the electrode. The cathode 1 satisfies a condition (a) or a condition (b) as follows and the anode 2 satisfies the condition (a) or the condition (b). A hollow portion in (a) and a space in (b) form a flow passage for a fluid that is supplied by a fluid supply device 5. The condition (a) is that the electrode comprises a hollow portion including an open end at the side of the clearance, and the condition (b) is that the insulation material is provided so as to enclose an outer periphery of the electrode with a space including an open end at the side of the clearance.SELECTED DRAWING: Figure 1【課題】従来の大気プラズマ発生装置や水中プラズマ発生装置よりも高い反応効率で被処理水を処理することができるプラズマ発生装置、窒素源製造装置、養液供給装置、育成システム、植物栽培システム、窒素源を製造する方法、及び二酸化炭素を還元する方法を提供する。【解決手段】陰極１と陽極２とを含むプラズマ発生装置であって、陰極１と陽極２とは、両者の間に電圧を印加することによりプラズマが発生する間隙を空けて配されており、陰極１及び陽極２は、電極と、電極を被覆する絶縁材とを含み、陰極１は、下記（ａ）又は下記（ｂ）であり、陽極２は、下記（ａ）又は下記（ｂ）である。そして、（ａ）における中空部及び（ｂ）における空間は、流体供給装置５により供給される流体の流路をなす。（ａ）電極が、間隙側に開口端がある中空部を有すること。（ｂ）絶縁材が、電極の外周を、間隙側に開口端がある空間を介して囲むように設けられていること。【選択図】図１
