PURPOSE: To solve a problem of defective transfer of a patterned part or a warp of a board by cooling an edge part of a sheet under a state in contact with a stamper without the edge of the sheet being twisted, by making the outside of an effective sphere of the stamper thin.

CONSTITUTION: Outside spheres 4 of an effective part of a stamper 1 are provided on both sides of the effective part 3 of the stamper 1 and the outside region 4 is provided so that they come into contact with a thick neck part. The whole width of the stamper to be obtained by adding the widths of the effective part 3 of the stamper and the outside region 4 together is either identical with the width of the molded sheet or set up wider than the width of the molded sheet. As for a method to provide a thin sphere, either a method grinding only the fixed outside sphere of the stamper 1 or a method to obtain the stamper by transferring from a mother mask by swelling a position of the fixed outside sphere of a mother mask beforehand are recommendable.