A new cultivation system which operates under a super high magnetic field in the range of 0.5 to 7 Tesla was developed. In this reactor system, the effects of a high magnetic field on various biological reactions could be investigated not only under a homogeneous high magnetic field, but also under a gradient magnetic held. The maximum magnetic field gradient is 23 Tesla/m. Since the superconductive magnet was designed so as to significantly reduce the evaporation rates of liquid helium and nitrogen, operation is virtually maintenance-free compared with that in conventional superconductive magnets. The temperature of the reactor is controllable within the range of 10 to 70 degrees C (deviations of +/- 0.1 degrees C). When Escherichia coil B cells were grown at 37 degrees C, total cell number during the stationary phase was 70% higher under homogeneous 7 Tesla conditions than in the geomagnetic field. A three fold larger cell number was detected in a gradient magnetic fields between 5 and 6 Tesla.