The present invention provides a lamp device comprising: a glass tube configured to cover a discharge space in which a pair of electrodes are arranged so as to face each other; and a bayonet cap portion provided in an end portion of the glass tube and electrically connected to one electrode of the pair of electrodes, wherein the bayonet cap portion is formed to have a shape including a bottom surface and a peripheral surface, and includes, in the bottom surface, a first opening configured to supply a gas to an inside of the bayonet cap portion and a second opening configured to exhaust the gas from the inside of the bayonet cap portion.