Antenna device

The present invention is provided with: a ground conductor (1); a dielectric tube (2) having ionizing gas therein, the dielectric tube passing through the ground conductor (1) such that a turned-back section (201) and both ends of the dielectric tube are disposed with the ground conductor (1) as a boundary; first electrode terminals (3, 4) provided at both ends of the dielectric tube (2); a plasma excitation power source (5) connected to the first electrode terminals (3, 4), the plasma excitation power source (5) converting the ionizing gas to a plasma state; an annular second electrode terminal (6) fitted so as to contact the outer circumference of the dielectric tube (2) closer to both end sides of the dielectric tube (2) than the ground conductor (1); a high-frequency transmitter (7) for supplying a high-frequency signal to the second electrode terminal (6); and a power supply line (8) connecting the second electrode terminal (6) and the high-frequency transmitter (7); the inner diameter of both ends of the dielectric tube (2) being larger than the inner diameter of the second electrode terminal (6).