NOVELTY - The apparatus (10) has an electronic device whose dew condensation stimulation part (12) carries out plasmon absorption of a part of light, which is irradiated by a light source (21). A light-receiving part (22) receives reflected light by the dew condensation stimulation part and transmitted light. A liquid condensation analysis part (32) analyzes condensation of liquid on the dew condensation stimulation part based on the reflected light and the transmitted light received by the light-receiving part. A sealing member (13) seals the dew condensation stimulation part of the electronic device.    USE - Apparatus for measuring water-vapor-permeation performance of a sealing member i.e. bonding resin member, utilized for sealing an electronic device such as solar cell device and organic electroluminescence (EL) device (all claimed). Can also be used as a moisture-content sensor in physical property measurement of a sealing member.    ADVANTAGE - The sealing member can seal the dew condensation stimulation part of the electronic device in a simple and effective manner. The apparatus can measure water vapor permeability variation of the sealing member in various environmental conditions such as high-temperature and high-humidity states, with high precision in real time. The apparatus can be used for evaluating moisture-proof performance of the sealing member, so that composition optimization can be performed easily. The dew condensation stimulation part is sealed with the electronic device, so that performance degradation of the electronic device is identified easily when measuring the moisture content at an inner side of the sealing member, thus prolonging service life of the electronic device.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for measuring water-vapor-permeation performance of a sealing member.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of a water-vapor-permeation measuring apparatus. '(Drawing includes non-English language text)'    Apparatus for measuring water-vapor-permeation performance (10)    Dew condensation stimulation part (12)    Sealing member (13)    Solar cell device (14)    Light source (21)    Light-receiving part (22)    Liquid condensation analysis part (32)