To provide an electric double layer capacitor which uses a packaged case made of stainless steel and has a low internal resistance and a high output density.

In the electric double layer capacitor, a pair of a polarized electrode composed of a carbon material containing an aqueous electrolyte and a collector is disposed via a separator so as to oppose one another, and an electric double layer capacitor element 2 of a structure with sealed outer periphery is sealed with a packaged case 31 made of stainless steel. A bottom 31a inside the packaged case 31 made of stainless steel is roughened by a laser processing in an inert gas atmosphere, and the element 2 is inserted into the roughened packaged case 31 made of stainless steel. An insulating case 32 for preventing a contact short between the element 2 and the packaged case 31 made of stainless steel is disposed in an opening of the packaged case 31 made of stainless steel, and a lead terminal (positive electrode) 33 and a lead terminal (negative terminal) 34 are disposed for extracting an electrode from the element 2. The packaged case 31 made of stainless steel is caulked and sealed, thereby forming a structure that the element 2 is pressured and held.