To fusion bond securely on a container main body of an easy opening container and secure sufficiently transparency and easy opening properties of peeling off easily from the container main body.

A cap 10 fusion bonded by utilizing a flange section or the like and unsealed by peeling off and destroying a fusion bonded section is formed into a three-layer structure formed of an outer material layer 11 forming an outer surface, a bonding layer 12 inside the outer material layer and an inner material layer 13 integrated with the outer material layer 11 through bonding layer 12, and a sheet material of 100-400 μm total thickness is formed by the arrangement, and as a material for the outer material layer 11, amorphous polyethylene terephthalate, biaxially oriented polystyrene, polycarbonate, polyvinyl chloride or polypropylene is adopted, while as a material for the inner material layer 13, monoaxially oriented polypropylene or the like is adopted.