PURPOSE: To seal up a joint between two metal cases making their openings butt against each other while the cases are compressed so as to obtain an electric double-layer capacitor which is able to cope with cleaning and use in a high vacuum.

CONSTITUTION: A metal case 2a is arranged on the upside of an electric double- layer capacitive element laminate 1 through the intermediary of an electrode plate 4a and an insulating case 3a, a metal case 2b equipped with hermetically sealed outer terminals 6a and 6b is provided to the base of the laminate 1 through the intermediary of an insulating plate 4b and an insulating case 3b, and the electrode plates 4a and 4b and the outer electrodes 3a and 3b are electrically connected together with lead wires 5a and 5b respectively. The junction of the metal cases 2a and 2b arranged on the upside and underside of the laminate 1 respectively is welded.