A jacket material into which a gas adsorbing device and core material are inserted is decompressed in a vacuum chamber, the opening is sealed, and then the jacket material is exposed to the atmosphere. In the atmospheric pressure, a pressure of about 1 atm which is equivalent to the pressure difference between the inside and outside is applied to the jacket material of the heat insulator. The jacket material is made of a plastic laminated film and is deformed by pressure. A protruding portion is plunged into a container to drill through holes, and a gas adsorbent in the container communicates with the inside of the jacket material. Thus, both during holding and in applying to the vacuum heat insulator, the gas adsorbent can be applied to the vacuum heat insulator without degradation, and the high degree of vacuum can be kept for a long time.