PURPOSE: To permit easy maintenance of heat exchanging blocks by successively providing the plural heat exchanging blocks which are vertically divided in parallel with the axial line of a cooler casing in the peripheral direction along the inside surface of the casing.

CONSTITUTION: The cooling gas flowing from a vacuum heating furnace into an inflow port 21 is conducted to a space 23 from which the cooling gas is guided by a flow dividing plate 25 and is conducted to a space 26 between the cooler casing 20 and the heat exchanging block 22 thereby cooling the device. The cooling gas is further passed through the heat exchanging block 22 and is conducted to a central space 24 and is cooled down to an adequate temp.; thereafter the cooling gas is sucked by a fan body 14 and is circulated through an outflow port 31 to the vacuum heating furnace. The flanges between the fan casing 15 and the cooler unit casing 20 are disconnected and only the heat exchanging block 22 necessary for maintenance is drawn out; then the maintenance operation thereof is carried out in the case of maintaining any one of the above-mentioned heat exchanging blocks 22. Easy maintenance operation is thus made possible.