PURPOSE: To provide a manufacturing method of a die for membrane for low temp. tank, by which the membrane having the same length in any direction along the surface, smooth heat shrinkage, suitable press workability, a little expansion and contraction at the time of pressing and corrugated crossing part can be manufactured.

CONSTITUTION: A lower die 10 having the upper surface matched with the lower surface of the membrane except the membrane crossing part is horizontally set and flexible sheets 14 having almost the same thickness as the membrane are horizontally laminated on the upper surface of the lower die. An upper die 12 having the lower surface matched with the upper surface of the corrugation except the crossing part is pushed to the upper surface of the flexible sheets 14, and by this method, the flexible sheets 14 are held to the shape of the membrane except the crossing part. Successively, a loose part positioned at the membrane crossing part in the flexible sheets is arranged to the shape being suitable to the press forming, and the die for pressing followed to the membrane crossing part of the flexible sheet is manufactured.