PURPOSE: To reduce sharply a leakage magnetic field from a window part by disposing a solenoid coil around a window frame of a window for a magnetic shield room and by making the coil generate a magnetic field canceling the leakage magnetic field from a ferromagnetic field generating apparatus in the room to the window part.

CONSTITUTION: A room wherein an apparatus generating a ferromagnetic field, such as a magnetic resonance diagnostic apparatus (MRI), is installed in provided with a wall finishing material 1, a magnetic shield material 2, a wave shield panel 3 and further backing H steel 4 between the finishing material 1 and the shield material 2, from the outside of a peripheral wall inward. A solenoid coil 8 is disposed in the wall part around a window frame 6, and a DC power source 9 is connected to the coil 8 so that the coil 8 generates a magnetic field canceling a leakage magnetic field from the MRI or the like to a window part. The coil 8 is so constituted that it can vary the magnitude of the magnetic field according to the amplitude of a current supplied thereto and also can vary the direction of the magnetic field according to the direction of the current. The magnitude and direction of the leakage magnetic field at the time when the MRI is used are measured by sensors and the current supplied is adjusted so that it be fitted for canceling the leakage magnetic field in the window part.