To provide a vacuum dryer 1 capable of automatically stopping when the drying degree reaches a prescribed value.

The temperature of a steam discharge tube 15 disposed between a processing tank 8 and a condensation means 11 rises after the drying process is started to the steady condition, and after that, the temperature begins to lower as the drying degree of a processed object W is lowered, that is, as the quantity of the discharged steam is reduced. Accordingly, if the relational expression between the temperature of the steam discharge tube 15 and the drying degree of the processed object W is previously found, the drying of the processed object W can be finished with a required value of the drying degree by automatically stopping the operation of the vacuum dryer 1 based on the value detected by a temperature sensor 16 mounted on the steam discharge tube 15.