To provide a discharge tube capable of generating discharges at a specified potential stably in repetitions.

A discharge tube includes an air-tight cylinder 10 furnished in the center of its inner wall with a first discharge trigger line 50 approx. parallel with a metallized surface 40 formed on the top face of the cylinder 10 in a loop form in such a way as crossing the inner wall of the cylinder 10. In the upper and the lower inner wall, the cylinder 10 is also furnished with second discharge trigger lines 60 in a loop form in such a way as drawing a wave and crossing the inner wall of the cylinder 10. The top of this wave of each second discharge trigger line 60 is connected to the metallized surface 40 formed on the top and the bottom face of the cylinder 10 located near. Electric discharge at a specified potential is stably generated in repetition between the discharge surface 23 at the forefront of the upper discharge electrode and the discharge surface 25 at the forefront of the lower discharge electrode, the two being located inside the cylinder 10 in such a way as opposing in its center.