The present invention relates to a gas discharge tube or the like having a structure for enabling the maintenance of discharge startability and the prevention of the shortening of the life of an anode section and for increasing the amount of visible light from a visible light source passing through a discharge path restricting section. The gas discharge tube comprises a sealed vessel in which gas is encapsulated. A cathode section and anode section for generating discharge are arranged in the sealed vessel. Furthermore, a discharge path restricting section for narrowing a discharge path is arranged between the cathode section and the anode section. In particular, an opening portion is formed in the anode section, and the cross section of the opening portion has a non-circular shape where the maximum opening width in a first direction is different from that in a second direction orthogonal to the first direction. Thus, the amount of the visible light passing through the opening portion of the anode section in the gas discharge tube from the visible light source can be increased by making the maximum opening width in one direction of the first and second directions longer than that in the other direction. The maintenance of the discharge startability and the prevention of the shortening of the life of the anode section can be attained by making the maximum opening width in the other direction shorter than that in one direction.