Dehydration method

A dehydration method comprising the steps of:nproviding a distilled process-target fluid to a water separation membrane device via a heat exchanger, the process-target fluid consisting of a mixture comprising ethanol and water or a mixture comprising propanol and water;separating the process-target fluid into a dehydrated product and water by using the water separation membrane device;detecting a temperature of any one of the water separation membrane device and the process-target fluid supplied to the water separation membrane device by using a temperature monitoring device provided on the membrane; andcontrolling the temperature of the process-target fluid so that the temperature of the distilled process-target fluid being maintained at a temperature higher than the condensation temperature of the distillate by 5 to 10° C. by using a temperature adjustment device provided in the water separation membrane device, the temperature adjustment device is a heat-medium flow rate controller which controls the amount of the heat medium into the heat exchanger on the basis of the temperature detected by the temperature monitoring device to optimize an amount of water permeation in a separation process in the water separation membrane device, whereinthe process-target fluid is a gaseous distillate or a liquid distillate obtained by distilling a raw material in a distillation tower,andthe distillation tower has a structure, where steam is supplied at a bottom portion, the raw material supplied to a middle portion is heated, and a concentrated raw material is distilled from a top portion of the distillation tower.