To enhance the heat efficiency and production efficiency utilizing waste-heat air, waste gas, etc., by senselessly lowering the heat-transfer coefficient with respect to the thickness.

A plurality of disks 8 rotating in a drying space 7 are solid and store the heat of the waste gas introduced into the drying space 7. Heat is exchanged between the raw liq. to be dried and the disk on the surface of the disk 8. The geometrical direction leading to a discharge port from a feed port is practically parallel to the revolving surface of each of the plurality of disks, and the hot air is strightened among many disks. A thicker disk is desirable unlike the conventional fin. The heat-exchange efficiency is increased by the thicker disk. The disk is preferably made of a titanium alloy from the standpoint of acid resistance and thermal conductivity.