Disclosed is a polymer electrolyte battery affording a high capacity density in which a layer of electrode active material mixture containing a polymer has an adequately regulated porosity and/or polymer content. The battery includes a unitary, laminated battery sheet composed of a negative electrode combined with positive electrodes, with a porous polymer separator being placed on both surfaces of the negative electrode. Each of the electrodes comprises a current collector and a layer of active material mixture disposed on both surfaces of the current collector, and the polymer is capable of absorbing and retaining nonaqueous electrolyte. The separator and the layer of electrode active material mixture have a porosity of 30 to 60%. Preferable polymer contents in the layer of active material mixture are in a range of 5 to 10 wt % for the positive electrode and in a range of 7 to 16 wt % for the negative electrode.