PURPOSE: To decrease the contact resistance between a conductive separator and an outer package case and to obtain a small equivalent series resistance even if the pressure at the time of caulking and sealing of a port by providing the outer package case whose bottom surface in contact with the surface of the conductor separator is machined in an irregular shape.

CONSTITUTION: An electric double-layer capacitor element 5a is constituted of the following parts: an iron transmitting and non-electron-conducting porous separator 11, a pair of paste electrode layers 10 which are separated through the porous separator 11, ion impermeable and electron conducting conductive separators 8 which are arranged through the paste electrode layers 10 and nonconducting gaskets 9 which are provided at the peripheral part of the above described pair of the paste electrode layers 10 between the conductive separators 8. A laminated body 5 of the electric double-layer capacitor elements 5a is contained in an outer package case 4. Thus an electric double-layer capacitor is obtained. In this capacitor, the bottom surface of the outer package case 4 which is in contact with the surface of the conductive separator 8 is machined in an irregular shape. For example, the outer package case 4 wherein protruding parts having the height of 0.2mm and the width of 0.5mm are machined in the concentric circles having the diameters of 2mm, 3.5mm and 5mm is used.