A model for a dehumidifying device using a solid polymer electrolyte membrane (Nafion 117, Dupont) is proposed. The dehumidifier in the model is represented by a physical model composed of a two-layer membrane and electrodes on the membrane surfaces. Measurement of the membrane weight shows that the ratio of the water content of the membrane to humidity in the surrounding air is a function of temperature under equilibrium conditions. The results for the water ratio are used for determining the parameters required for the modeling. The electrical resistance of the dehumidifier was measured and is given as a function of temperature and the membrane water content. Simulation of the characteristics of the dehumidifying device is presented and the results are found to agree with the measured characteristics of the device. We also report an attempt to determine the parameters describing the dehumidifying processes.