To obtain a double-layer electric capacitor having enlarged volume utilizing efficiency by conductively connecting a plurality of unit capacitors covered by a cladding body consisting of synthetic resin or a complex of syn thetic resin and a metal and sealed for being housed inside a sealed container so as to have an enlarged volume utilizing efficiency.

Individual capacitors A1 to A3 are airtightly cladded by cladding bodies. At the time of airtightly cladding respective unit capacitors with cladding bodies, positive and negative terminals P1 to P3, N1 to N3 are in advance drawn out. Then, respective unit capacitors A1 to A3 are connected in series or in parallel by wirings W to PT, NT and housed in a container C in this state. Double-layer electric capacitors using an organic electrolyte have to avoid intrusion even of a trace amount of moisture so as to necessitate it to be given an airtight seal of synthetic resin to the unit capacitors A1 to A3.