PURPOSE: To prevent the infiltration of moisture by inserting a power generating element between a pair of sheet-like terminal plates, hermetically sealing the peripheral section with an electrical insulating film coated with a heat sensing adhesive, and coating its vicinity with moistureproof paint.

CONSTITUTION: In a flat type nonaqueous electrolyte cell, a positive electrode black mix 3, a separator layer 4, and a negative electrode layer 5 are inserted in lamination between a pair of sheet-like terminal plates 1, 2; the peripheral section is hermetically sealed with an electrical insulating film 6 coated with a heat sensing adhesive; and further the vicinities of the side section and the upper and lower surfaces are coated with solvent type polyurethane-series moistureproof paint or ultraviolet ray hardening type acrylic resin to form a moistureproof coated film at the thickness of 0.02∼0.1mm. Accordingly, the infiltration of moisture improved, and the quality can be stabilized for a long time.