PURPOSE: To prevent a shift of a heat insulating material by a method wherein a heat insulating plate fitted into a grid or a single heat insulating plate is mounted on a movable platen while being pressed by a pressing means for inhibiting the horizontal movement, and a gap is provided between a lowermost hot plate and the movable platen.

CONSTITUTION: Hot plates 5 are set on a plurality of step parts 4 of step plates 3, which are erected on a base mount of a hot press 1 on the both sides of a movable platen 2, in parallel to the movable platen 2. On the top surface of the movable platen 2, a heat insulating plate 10a fitted into a rectangular grid 8 (or a single heat insulating plate) is provided. The grid 8 is pressed from the side faces thereof through leaf springs 9 projected from the upper side faces of the movable platen 2. In this manner, the heat insulating plate 10a is inhibited from moving horizontally out of the movable platen 2. The height of the step part 4 is so determined that a gap can be formed between the surface of the heat insulating plate 10a and the lowermost hot plate 5a.