PURPOSE: To prevent the failure of a semiconductor element accompanying a lack of drying, and to enable the stabilization of functions by monitoring the dried state of wafers to control them to a suitable dried state.

CONSTITUTION: A rotary bath 2 contains wafers 1 to rotate them at a 500-2000RPM, thereby removing moisture deposited on the wafers 1 with centrifugal force. Further, this bath allows them to be dried by a spout of 50-500l/min drying gas from a nozzle 8. Water drops and drying gas are exhausted (drained) through an exhausted pipe 6 after measurement by humidity sensor 3. Sensed humidity is latched into a controller 4 for judgement of a dried state, where it controls the flow rate of drying gas and the number of rotation. The time of a rotation can be set within a period of 0-10min after humidity reaches a setpoint (0-30%).