To provide a heat insulation box with which repair work in a carbonization chamber is safely carried out without using cooling water and with protecting workmen and mineral variation of refractory is prevented by constantly holding temperature in the carbonization chamber except working area of the workmen.

In the heat insulation box, the upper face facing to the ceiling face of the carbonization chamber, the lower face facing the floor face of the carbonization chamber, a wider side face facing to the wall face without repairing, a narrower face facing to the wall face of the carbonization chamber requiring repairing and a lateral face facing to the end wall face of the coke oven are constituted of frame materials 6A-6R, a heat insulation material is filled in spaces among frame materials of the upper face, the wider side face, the narrower side face and the lateral face, and the surfaces of the heat insulation material are covered with a heat resistant stainless steel net.