Recently, for the repair of corroded or fatigue damaged steel members, bonding patch plate have been proposed and applied. One of the concerns of this method is prevention of debonding of patch plate, because the shear and peel stresses in adhsive layer concentrate at the end of patch plate. In this study, the equation for calculation of stresses in adhesive in single lap joint under tensil or bending condtion. Furthermore, the tensile test and bending test of single lap joint were carried out to evaluate the debonding condition with applying the adhesive stresses. As a result, it was shown that the energy release rate and principal stress calculated by the adhesive stresses are able to evaluate the debonding of patch plate under tensile load or bending.