PURPOSE: To improve a cycle characteristic Coulomb efficiency of charge- discharge and capacity by using a carbonized material of a specific polyimide type polymer as a negative electrode, and using a molding containing activated carbon as a positive electrode.

CONSTITUTION: A polyimide type polymer having a formula (R is a tetravalent aromatic residual group having at least one aromatic ring, and each bivalence among it joins to adjacent C in an aromatic ring by making a pair, and (n) is not less than 2), is heated and carbonized at 500 to 1500°C in a nonoxidizing atmosphere, and a carbonized material of a polyimide type polymer on which the atomic ratio (N/C) of nitrogen to carbon is 0.001 to 0.100 and lattice spacing [d(002)] of X-ray diffraction is 3.58 to 4.10, is obtained. This carbonized material 98 to 60wt.% and resin 2 to 40wt.% for a binder are mixed together, and a molding obtained by molding is used as a negative electrode, and a molding containing activated charcoal having the specific surface area (a BET method) not less than 500m2/g is used as a positive electrode.