To produce a molding having a better quality by a method wherein the forming time of a thick heat-insulating member can be reduced and, at the same time, the temperature of the thick heat-insulating member at its forming can be made constant.

A thick heat insulating member S is brought under a nearly enclosed state by means of a silicone rubber sheet 33, which is pinchingly fixed to a sheet frame 32, and a main body 31 at a vacuum molding part 30 so as to supply a negative pressure to this nearly enclosed space in order to form by elongatingly deforming the silicone rubber sheet. At this time, a radiation heating part 40 is faced to the silicone rubber sheet 33 for the predetermined heating so as to indirectly heat and, at the same time, soften the thicker heat insulating member S in order to form under the utilization of the elongation deformation of the silicone rubber sheet 33 due to the above negative pressure, resulting in making the remarkable reduction of the forming time of the thicker heat insulating member S possible.