An atmospheric pressure plasma generator comprising: an approximately cylindrical housing having an inner circumferential surface with a small diameter section and a large diameter section, a diameter of the large diameter section being larger than a diameter of the small diameter section; a tubular outer tube, its outer diameter being slightly smaller than an inner diameter of the large diameter section such that the outer tube is engaged into the large diameter section of the housing and an end of the tubular outer tube protrudes from an end section of the housing on the large diameter section side; an inner tube, with an outer diameter smaller than an inner diameter of the outer tube, the inner tube is inserted into the small diameter section of the housing, so that the end of the inner tube protrudes slightly from the end section of the housing on the large diameter section side, wherein the protruding amount of the tubular outer tube from the end section of the housing on the large diameter section side is larger than the protruding amount of the inner tube from the end section of the housing on the large diameter section side, the inner tube being formed from a material with either positive or negative electrical charging polarity, being a material, which is, in a case of static electricity caused by friction, charged as either an anode or a cathode; only one electrode, the electrode being capable to assume the electrical polarity opposite to that of the material of the inner tube, the electrode being provided on an outer circumferential surface of the outer tube, a first flow path inside the inner tube, and a second flow path between an outer circumferential surface of the inner tube and an inner circumferential surface of the outer tube, wherein in operation, a processing gas is arranged to flow in at least one of the first flow path and the second flow path, and the processing gas by contact is arranged to electrically charge the inner tube, such that by applying an electric current to the electrode, an electrical discharge is arranged to occur between the electrode and the inner tube capable to plasmarize the processing gas. an approximately cylindrical housing having an inner circumferential surface with a small diameter section and a large diameter section, a diameter of the large diameter section being larger than a diameter of the small diameter section; a tubular outer tube, its outer diameter being slightly smaller than an inner diameter of the large diameter section such that the outer tube is engaged into the large diameter section of the housing and an end of the tubular outer tube protrudes from an end section of the housing on the large diameter section side; an inner tube, with an outer diameter smaller than an inner diameter of the outer tube, the inner tube is inserted into the small diameter section of the housing, so that the end of the inner tube protrudes slightly from the end section of the housing on the large diameter section side, wherein the protruding amount of the tubular outer tube from the end section of the housing on the large diameter section side is larger than the protruding amount of the inner tube from the end section of the housing on the large diameter section side, the inner tube being formed from a material with either positive or negative electrical charging polarity, being a material, which is, in a case of static electricity caused by friction, charged as either an anode or a cathode; only one electrode, the electrode being capable to assume the electrical polarity opposite to that of the material of the inner tube, the electrode being provided on an outer circumferential surface of the outer tube, a first flow path inside the inner tube, and a second flow path between an outer circumferential surface of the inner tube and an inner circumferential surface of the outer tube, wherein in operation, a processing gas is arranged to flow in at least one of the first flow path and the second flow path, and the processing gas by contact is arranged to electrically charge the inner tube, such that by applying an electric current to the electrode, an electrical discharge is arranged to occur between the electrode and the inner tube capable to plasmarize the processing gas.