A sealant film has a structure made of a laminated body of two or more layers. The laminated body includes a first resin layer 7 containing 50 mass % or more of a random copolymer containing propylene and a copolymer component other than propylene as copolymer components, and a second resin layer 8 formed by a mixed resin containing a first elastomer-modified olefin based resin having a melting point of 155° C. or higher and a crystal melting energy of 50 J/g or more, and a second elastomer-modified olefin based resin having a melting point is 135° C. or higher and a crystal melting energy of 30 J/g or less. With this structure, when the inner pressure of a power storage device is excessively increased, breakage (separation) occurs inside the sealant layer, causing gas-releasing, which in turn can prevent bursting of the packaging material due to the inner pressure increase.