PURPOSE: To retain a bent shape by bending an undrawing polypropylene sheet into a predetermined shape, fusing the bent part, and then cooling the fused part thereby varying the crystal structure thereat.

CONSTITUTION: A heater 2 is brought close to a part 1a being bent of a casting polypropylene sheet 1 to cause partial fusion along the part 1a being bent before bending the sheet 1. When the sheet 1 is cooled naturally under that state, the bend part 4 has crystal structure. Since the bent shape is retained as it is, a molded sheet excellent in shape-memory properties can be obtained.