A disclosed flat type lamp for a photoionization detector includes: a first plate member having a plate shape and having a first surface on which a plurality of discharge cavities is formed; a second plate member isolating the plurality of discharge cavities from the outside by being disposed and sealed on the first surface of the first plate member; electrodes disposed on the first and second plate members and arranged to face each other; and a discharge gas filled in the plurality of discharge cavities and producing vacuum ultraviolet using electric force that is applied through the electrodes.