Discharge tube

A discharge tube, comprising:

• a container in which a discharge gas is sealed;
• an anode portion made of a plate-shaped member in which an opening is formed, and disposed in the container;
• a cathode portion made of a plate-shaped member, disposed in the container to face the anode portion, and emitting photoelectrons in response to an incidence of light that has passed through the opening;
• an anode electrode portion having a rod shape, extending along a facing direction in which the anode portion and the cathode portion face each other, and joined to the anode portion;
• and
• a cathode electrode portion having a rod shape, extending along the facing direction, and joined to the cathode portion,
• wherein, when a side on which the anode portion is located with respect to the cathode portion in the facing direction in which the anode portion and the cathode portion face each other is defined as one side, and a side opposite the one side is defined as the other side, the anode electrode portion extends from the anode portion to the other side, and the cathode electrode portion extends from the cathode portion to the other side, and
• a joint region of the cathode portion with the cathode electrode portion is exposed from the anode portion when viewed from the one side in the facing direction.