PURPOSE: To improve a heat insulating enclosure for reducing the heat loss of a heated material block.

CONSTITUTION: The heat insulating enclosure is composed of heat insulating means 10, 20 provided with heat insulating member group 22 held with the top covers 10, 70, and the member 22 group is hung down in free state, so as to allow relatively variation between the members 22 and the cover. The member 22 group is hung down to the different level below the cover and a screen 24 is formed in the inner part of the enclosure to reduce the free space in the inner part thereof, and the cover covering at least the upper surface of the hot block is provided. The member screen can flexibly be varied so as to be possible to cover the hot block for retaining the heat in the max. limit.