A discharge tube comprises a pair of discharge electrodes opposed to each other with a discharge space in-between, an airtight cylinder in which the discharge space is formed, the pair of the electrodes respectively being mounted on both ends of the airtight cylinder, and a coating film which is resistant to water permeation, and formed on a surface of the airtight cylinder. With the discharge tube, it is possible to perform a stable discharge having a good insulating property between the discharge electrodes even when the external environment changes.
