The four shift bump magnets (BUHS01-04) of the 3-GeV RCS in J-PARC, which are located at the long straight section, produce a fixed main bump orbit to merge the injection beam into the circulating beam. They are realized with four magnets connected in series to form the accurate closed bump orbit. However, the total integrated magnetic field of the four magnets is not zero because of the magnetic field interference between the shift bump magnet and the adjacent quadrupole magnets (Q magnet). In order to measure the magnetic field distribution accurately, the short search coil and the long search coil were used. Furthermore, the imbalance of the total integrated magnetic field has been improvement by inserting 0.3 mm insulators in the median plane of the return yoke of the BUHS02 and 03. The value of the integration has been decreased from 2358.0 G · cm to -71.6 G · cm. © 2008 IEEE.