PURPOSE: To reduce heat loss, and efficiently heat a work to be treated by a method wherein a supporting pillar for the work to be treated is established at the central part of a truck and heat insulating covers are hung from both of left-and-right sides of the pillar, in the truck putting the work thereon and carrying it in the main body of an oven.

CONSTITUTION: A heat treatment oven 1 is provided with heat ducts 3 at both of left-and-right sides of the inside of the main body 2 of the oven. A work W to be treated is put on a truck 5 of a floor conveyer 4 to carry it in the main body 2 of the oven. In this case, a supporting pillar 6, supporting the work W thereabove, is established at the central part of the truck 5. An attachment 7 for supporting both of left-and-right ends of the work W is provided at the upper part of the supporting pillar 6. Further, a pair of left and light heat insulating covers 8 are arranged on a floor wall 9 so as to pinch the supporting pillar 6 from both of left-and-right sides. According to this method, heat loss in the main body 2 of the oven is reduced whereby the rise-up time of the heat treatment oven 1 is shortened while the work W can be heated efficiently without heating the truck 5.