Abstract: In an ionization chamber detector of the type in which a plurality of flat anode and cathode electrodes are alternately arranged in a predetermined gaseous medium, this invention provides a method of producing an ionization chamber detector which is characterized in that a plurality of ditches having a width a little bit greater than the thickness of the electrodes are formed on the inner surfaces of a pair of insulators disposed in the spaced-apart relation for supporting and fixing the anode and cathode electrodes, an adhesive is applied in advance temporarily in a rectangular form to both or one surface of each electrode at those positions which are set back by a distance corresponding to the thickness of the electrodes from both edge portions, another adhesive having a low viscosity is charged from the end portions of the ditches into the gaps between the electrodes and the ditch walls after the electrodes are inserted into the ditches, and the tentative adhesive and the adhesive having a low viscosity ar