PURPOSE: To obtain a dried cake immediately from a dehydrator and further, obtain a thoroughly dehydrated dry cake without returning separated moisture into the cake by injecting sludge into an airtight filter chamber forcibly and pressing it into a cake, and taking out the cake after blowing a high temperature gas at high pressure into the generated cake.

CONSTITUTION: Each filter plate 3 is opened to form a filter chamber between the filter plates 3 using filter cloths 6, 6, and sludge is pressed into the filter chamber and dehydrated there. In addition, a high-temperature gas at high pressure is blown into a cake generated in the filter chamber from a filtrate delivery passage 14. That is, the cake pressed into the filter chamber and dehydrated is heated by the high temperature, high pressure gas, resulting in the evaporation of moisture. The evaporated moisture, in turn, passes through a liquid passage 13 to be discharged to an area outside a device and dried there. In addition, the cake is heated in the airtight filter chamber so that the heat of a hot gas can be used efficiently without allowing it to escape to an area outside the filter chamber, and the evaporated moisture is discharged to an area outside the device. Thus the moisture is completely separated from the cake, and the cake is maintained at high temperature even after taking it out, and is left to dry up due to the continued evaporation of moisture.