An MRI apparatus which employs an open superconducting magnet, cancels fluctuation of the static magnetic field caused by vibration, and has uniform and temporally stable magnetic field. This MRI apparatus comprises a static magnetic field generating magnet having magnetic field generating sources so disposed as to hold there between an image pickup space in which a subject is placed and magnetic field fluctuation reducing plates respectively disposed inside thereof. A gradient magnetic field coil is fixed to the static magnetic field generating magnet out of contact with the magnetic field fluctuation reducing plates. When the intensity of the magnetic field generated by the static magnetic field generating magnet is changed because of the vibration of the gradient magnetic field coil or the like while the MRI apparatus is operating, eddy current corresponding to the fluctuating component of the magnetic field is generated in the magnetic field fluctuation reducing plates. A magnetic flux canceling the static magnetic field fluctuating component is generated by the eddy current, and, as a result, temporally stable static magnetic field can be obtained.