Safety of fill-dam gallery is evaluated with AFOSM and PEM. The design sections based on serviceability limit state of thermal stress and allowable stress method are checked. As a result, the both sections have safety indices over 4 in ultimate limit state, then show enough safety. Especially, the amount of reinforcement in serviceability limit state of thermal stress is over-estimated. It is found that the proper amount of reinforcement is about O.2% at arch crown. Moreover, the partial safety factors on limit state design in Japan are reasonable values, if allowable safety index β_a = 4 and coefficient of variation with external load is lO%.