PURPOSE: To obtain an electric double layer capacitor of long life by composing a metallic case or a metallic covering body out of a stainless steel including Cr or Ni and allowing that to include at least Sn.

CONSTITUTION: For both metallic case 3 and metallic covering body 4, a stainless steel consisting of Ni of 10 - 12 wt.%, CR of 18 - 20 wt.%, Mo of 0.5 - 0.8 wt.%, Co of 0.002 - 0.005 wt.% and Sn 0.1 - 0.2 wt.% is used. Then, a coin- type electric double layer capacitor is manufactured.