PURPOSE: To reduce the driving load of belts and prevent the endless belts and the inner wall of a pressure vessel from being damaged by a structure wherein sliding members are fixed in a pressure vessel at positions at which both the upper and lower belts come into contact with the pressure vessel.

CONSTITUTION: A pressure vessel 3 consists of an upper pressure vessel 1 and a lower pressure vessel 2. Molten liquid-like pressure medium is housed in the interior of the heating zone 4 at the middle of the pressure vessel 3. Laminated material 5 is moved under the condition being pinched by metallic endless belts 6, from the inlet zone 9 to the outlet zone 10 so as to be passed through the heating zone during its movement. Over the whole length ranging from the inlet zone 9 to the outlet zone 10 of the pressure vessel, sliding members 12 are fixed at positions, at which both the upper and lower belts 6 come into contact with the pressure vessel 3, to the pressure vessel 3. The sliding member must have the hardness which gives no damage to the endless belt such as that of graphite plate, the heat conductivity which easily transmits the heat of the pressure medium to the laminated material, low frictional resistance and heat resistance. The sliding members are fixed onto the inner wall of the pressure vessel through mounting bolts with fixing washers 13 by abutting the projecting part of each washer against the recess, which is provided at the periphery of each unit sliding member.