In recent society, the lap joint that is one of the joint techniques in the industrial society is used for the purpose of joint with the material and the material or the material and the metal and dissimilar materials. We are given the favor in the daily life for the merchandise, the tool and the other goods. The studies of concerning of the lap joint such as the analysis of the surface for the adhesive and the adherent are reported. There is much report about the FEM, but the experimental analysis is not much. Especially, the thermal stress analysis of the lap joint is reported a few. These are almost about the FEM methods, but the report of the thermal analysis is few. The authors think that the experimental analysis is not enough about the study of the thermal analysis and tried to experiment the stress of the adherent. Therefore the authors tried to analyze using the photoelasticity methods. The authors made for the device to analyze the under same temperature of around the circumstance. This new device keeps the temperature constantly; the adhesive and the adherent are keeping in this device. This was observed the variation of the stress under constant temperature. It was obtained the result that the stress of the adhesive joint was influenced about the heat.