To provide a reduced pressure dehydration treatment method which attains efficient dehydration treatment.

A mixture before drying is fed into a cooker 1 disposed with a stirring disk 15 at the inside via a first snake pump 6 while retaining the pressure-reduced state in the cooker 1 and further, the mixture after drying is exhausted from a cooker receiving tank 5 while retaining the evacuated state of the cooker 1 via a second snake pump 7 after the passage of a prescribed time from the feed of the mixture before drying.