Disclosed is a vacuum heat insulating material. Also disclosed is a heat insulating box using the vacuum heat insulating material. The vacuum heat insulating material includes a core member and envelope members having gas-barrier properties and including heat-seal layers. The envelope members are opposed to each other in such a manner that the core member is disposed between the heat-seal layers. The envelope members are entirely heated to a temperature at which the heat-seal layers are melted, and the heat-seal layers are heat sealed to each other by applying uniform pressure to the entire envelope members from outside to inside the envelope members.