The measurement and comparison of residual stress on welding line of common block butt and master butt on side shell and upper deck (As restraint is not free in reality, it is locked in stress) was made for the actual ship of 40, 000 D. W. oil tanker, and, at the same time, the measurement and comparison of reaction stress of block butt and master butt made adopting the idea of the intensity of restraint stated in the Report No. 1, and, also, by comparing and examining the difference between the above two, the safety of master butt was confirmed. Residual stress was computed based upon the result of the measurement of open strain which was made using the Gunnert Strain Gauge. As for reaction stress, the variation of strain was measured by means of Contact Strain Gauge and after that the order of reaction stress was estimated basing on the result of its measurement. From these measurement, the followings have been given as a conclusion : (1) There is almost no difference between the levels of residual stress on welding lines of master butt and common block butt on side shell and upper deck. (2) As regards common block butt and master butt on side shell, the measurement of reaction stress which shows their intensity of restraint was carried out on every points of blocks. As a result, it was proved that the order of reaction stress is nearly zero and the intensity of restraint low. (3) From the results stated in the above (1) and (2), it is judged that there will be no anxiety against the intensity of restraint of master butt in the Method of Erection Started Simultaneously at Several Locations which is adopted at our shipyard at present, provided that welding is properly done, and the master butt can be treated quite in the same way as in the case of common block butt.