PURPOSE: To provide a die for blow-molding which does not give a dimensional error to a product, and does not generate burr either by making at least one pair of peripheral wall members among a specified number of pairs of peripheral wall members movable diagonally downward in the confronted direction.

CONSTITUTION: A female die 1 consists of a flat square bottom member 21 which is arranged on a base board 20, and two pairs of, four peripheral wall members 24a, 24b, 26a, 26b which are located on four edges of the bottom member 21. One pair of members 24a, 24b among two pairs of the peripheral wall members can move in A direction by the actuation of hydraulic cylinders 25a, 25b, along guides 23a, 23b which are arranged on tilted surfaces 22a, 22b formed at both sides of the bottom member 21. The other pair of peripheral wall members 26a, 26b are arranged to be in contact with the bottom member 21. By this method, chattering due to the wear of parts does not generate, there is no gap at the joined part between the bottom member and peripheral wall members.