Influence of the magnetic field, which is produced around the JT-60 tokamak, on the performance of the neutral beam injector was experimentally studied using the stray field simulating coils installed around the prototype injector unit. Temperature distributions on the ion dump shifted vertically and the peak values changed in the presence of the field, as expected from the calculation of ion orbits. The shift length and the peak values remained within the permissible level, however, because of the operation of two cancellation coils, one of which was set around the reflecting magnet and another around the neutralizer magnetic shield. The neutral power injected into the beam target decreased by 4 to 5 % during application of the stray field due to the reionization loss of neutral particles. Under operating conditions, the heat load on each component was below the design value and all the components worked without any problems in the presence of stray magnetic field.