To provide a dehydrater for stably compressing and dehydrating wastes such as municipal wastes containing much water and mixed with solid wastes of metal, or the like, without an outbreak of a trouble suck as blocking.

In addition to provide a piston 2 for compressing the wastes 5 in the horizontal direction and an input port 7 for the wastes at one end of a horizontal hollow casing 1, and an exhaust port 9 for the compressed wastes at the other end of the casing 1, the dehydrater is includes drain holes 14 for squeezed water and a slidable pressure bulkhead plate 10 which receives the wastes compressed by the piston, both provided between the input port 7 and the exhaust port 9. Or, the casing 1 is a vertical cylinder wherein a rotating body is disposed in which a plurality of wastes compression chambers are allocated at prescribed intervals and a piston to compress the wastes is provided on the casing.