PURPOSE: To achieve an efficient removal of moisture, by providing a detector which is made up of a porous electrode, a proton conducting solid and a hydrogen occlusion alloy to generate quantity of electricity based on moisture in a gas.

CONSTITUTION: A porous electrode 9 causes a change of H2O→2H++1/202+2e-. Here, vapor pressure of water is given by P1=K[H2O]/[O2]1/2, wherein [H2O] is water vapor pressure and [O2]1/2 oxygen partial pressure and K constant. A hydrogen occlusion alloy 17 causes a change of 2H++2e-→H2, wherein a hydrogen partial pressure P2 is constant. Hence, a voltage output E is given by E=E0+RT/2F.lnP1=A+BlnP1, wherein R represents gas constant, E0 initial voltage and 2F movement of electric charge. Thus, the voltage output E changes based on a water vapor pressure P1. When moisture rises to exceed a specified value, a switch 21 conducts to apply a voltage between porous electrodes 9 and 11, thereby removing moisture within the equipment.