PURPOSE: To perform measurement even within the shaking of an airplane without receiving effect by mounting a pair of superconductive spheres floating by the magnetic field generated by a magnetic field generator and a position measuring device measuring the positions of the superconductive spheres.

CONSTITUTION: A magnetic field generator 1 generates a magnetic field satisfying the condition of formula at the arbitrary point of a vacuum container. By the magnetic field, the magnetic force acting on superconductive spheres 2 is well-balanced with average gravity in a vertical direction and zero in a horizontal direction. A position measuring device 3 measures the superconductive spheres 2 to the coordinates axis fixed to a measuring system. Since the rotary motion (high in frequency) of the shaking of the measuring system is suppressed by springs 5 and rotary spheres 6, a displacement detector compares the measuring result of two superconductive spheres to make it possible to obtain the difference between the gravities at points A, B. Therefore, the displacement of gravity can be measured even in the shaking of an airplane without receiving the effect of the shaking.