PURPOSE: To smoothly discharge the dehydrated substance without enlarging the erection height of a machine and also forming a bridge of the substance by freely turnably attaching a chord part pivotally to the diameter part of the bottom part of a dehydration tank and forming the bottom plate of two sheets of semidisk.

CONSTITUTION: When dehydration is completed after a dehydration tank 4 is rotated in a prescribed time, this tank 4 is rotated at low velocity and also a protrusion rod 30 is projected to the inside part by actuating a solenoid 31. Therefore, the protrusion rod 30 is allowed to abut against the lower end part of a hook 26 pivotally attached to the outside of the tank 4. Since the engaged piece 27 of a bottom plate 12 is detached from the engaging groove 26' of the hook 26, the bottom plate 12 of the tank 4 is opened and substance to be hydrated falls to the lower part and is discharged. Then, when discharge of the substance is finished, a ring 23 is lowered by rotation of a geared motor 16. The abutting piece 15 of a lever 14 is pushed down to the lower part and the bottom plate 12 is moved to the direction of closing 3.