PURPOSE: To obtain a drum dryer capable of operating with improved drying efficiency for a liquid raw material and reduced energy consumption by providing a main body of the drum dryer to which heat medium is fed to the inside, and a heat exchanger inserted into the main body of the drum and to which feed liquid is supplied.

CONSTITUTION: Feed liquid is introduced in the first place, into a heat exchanger 20 and preheated, then fed to an evaporator 42. Gas/liquid separation of the feed liquid is performed in the evaporator 42 and the concn. of the feed liquid is increased to some extent. The concentrated liquid is then fed to the surface of the main body of the drum 11 of the drum dryer from a nozzle 14 to proceed final drying by evaporation. The temp. of the feed liquid fed to the main body of the drum 11 is elevated by the preheating and the concentration. Since the water content of the feed liquid is decreased by these treatment, the heating surface can be lessened and the device can be miniaturized. Further, the steam separated in the evaporator 42 is discharged to the outside by an exhausting device 43.