A secondary battery in sheet type, which comprises; (a) an internal electrode pair in sheet type which is obtained by stacking alternately sheets of cathode electrode (1 a) and sheets of anode electrode (1 b) with separator between them, (b) a flexible envelope form package having a three layer laminated film that consists of an internal layer of thermoplastic resin, a middle layer of metal foil, and an external layer of resin, and containing inside hermetically the internal electrode pair and electrolyte, (c) a pair of internal leads (5a, 5b) that are respectively connected with separately each of cathode electrode and each of anode electrode of the internal electrode pair inside the envelope form package, (d) a pair of external leads (6a, 6b) that are provided on the outside of the envelope form package corresponding to each of the internal leads (5a, 5b) with the envelope form package in between, and (e) a pair of connecting means going through sealed penetrating holes of the envelope form package, one side of which is connected to each of the internal leads (5a, 5b) inside the envelope form package and the other side is connected to each of the external leads (6a, 6b) on the outside of the envelope form package as well so that each of the internal leads (5a, 5b) and each of the external leads (6a, 6b) are electrically connected, (f) a pair of sealing parts being installed between the internal leads (5a, 5b) and the envelope form package in order to seal penetrating holes of the envelope form package, and being made of synthetic resin which has chemical resistance; and (g) a pair of sealing parts being installed between the external leads (6a, 6b) and the envelope form package in order to seal the penetrating holes of the envelope form package, and being made of synthetic resin that has good electrical insulation. (a) an internal electrode pair in sheet type which is obtained by stacking alternately sheets of cathode electrode (1 a) and sheets of anode electrode (1 b) with separator between them, (b) a flexible envelope form package having a three layer laminated film that consists of an internal layer of thermoplastic resin, a middle layer of metal foil, and an external layer of resin, and containing inside hermetically the internal electrode pair and electrolyte, (c) a pair of internal leads (5a, 5b) that are respectively connected with separately each of cathode electrode and each of anode electrode of the internal electrode pair inside the envelope form package, (d) a pair of external leads (6a, 6b) that are provided on the outside of the envelope form package corresponding to each of the internal leads (5a, 5b) with the envelope form package in between, and (e) a pair of connecting means going through sealed penetrating holes of the envelope form package, one side of which is connected to each of the internal leads (5a, 5b) inside the envelope form package and the other side is connected to each of the external leads (6a, 6b) on the outside of the envelope form package as well so that each of the internal leads (5a, 5b) and each of the external leads (6a, 6b) are electrically connected, (f) a pair of sealing parts being installed between the internal leads (5a, 5b) and the envelope form package in order to seal penetrating holes of the envelope form package, and being made of synthetic resin which has chemical resistance; and (g) a pair of sealing parts being installed between the external leads (6a, 6b) and the envelope form package in order to seal the penetrating holes of the envelope form package, and being made of synthetic resin that has good electrical insulation.