PURPOSE: To reduce production of energy and time loss, by a method wherein a powdery material, such as peat, under an atmospheric pressure, is fed in a container in a condition to hold the pressure of a container under a pressure, and the dehydrated powdery material is discharged from the container to a place under an atmospheric pressure.

CONSTITUTION: A powdery material feeding and discharging device is provided between a feed hopper 13 and an inlet 3 of a reactor 1 and an outlet 4 of the reactor 1 and a discharge powdery material receiving part under an atmospheric pressure with ducts 17, 34 and pressure seal parts 20 and 37 having throttles 19, 35, and sluice valves 18, 36. The pressure seal parts 20 and 37 are provided with means 15, 16:32, 33 for feeding with a pressure a powdery material in the feed hopper 13 or the reactor 1. When the powdery material is fed with a pressure to the reactors 17 and 34 by means of the powdery material forced- feeding means 15, 16:32, 33, a forced pressure is generated between the powdery material and the inner surfaces of the ducts17 and 34 by means of the throttles 19 and 35, and this enables a pressure to be sufficiently sealed. In case a forced feed force is rendered ineffective, closing of the sluice valves 18 and 36 causes maintenance of sealing action.