<p>Disclosed is a secondary battery wherein a laminated film is used for a battery container and a good balance is achieved between high energy density and high strength of the battery itself. Specifically disclosed is a secondary battery which comprises an electric power generating element (1) and a packaging material for sealing the electric power generating element (1). The packaging material comprises a first multilayer composite sheet (2) having a first metal layer that is composed of stainless steel and a first plastic layer, and a second multilayer composite sheet (3) having a second metal layer that is mainly composed of aluminum and a second plastic layer. The second multilayer composite sheet (3) is provided with a recess that serves as a container portion for housing the electric power generating element (1). The first plastic layer of the first multilayer composite sheet (2) and the second plastic layer of the second multilayer composite sheet (3) are heat-welded with each other, so that the electric power generating element (1) is sealed within the packaging material.</p>
