The present invention aims to provide a method for forming a thermoplastic polymer sheet with an elasticized region adapted to be extensible and contractible in its thickness direction without an apprehension that the thermoplastic polymer sheet might be broken, and the sheet manufactured by this method. The present invention provides a method for forming a thermoplastic polymer sheet 10 at a distance from an outer peripheral edge 12 thereof with an elasticized region 11 adapted to be extensible and contractible in a thickness direction of the sheet using stationery mold 5 and movable mold 6 each having a plurality of forming blades 2, characterized in that a plurality of the forming blades are configured so as to have projected cross-sectional shapes on the sheet defined by similar curved lines and/or similar flexural lines arranged around a center of similitude and extending in the thickness direction of the sheet from the stationery mold and the movable mold so as to be engaged one with another but not to come in contact one with another, a step of introducing the sheet between the stationery mold and the movable mold and a step of bring the forming blades of the stationery mold and the movable mold into engagement with one another to stretch the sheet between distal ends of each pair of the adjacent forming blades. The sheet manufactured by this method is also provided.
