To provide a magnetic field generator for MRI which can be reduced in the weight and can be miniaturized although a vibration proofing mechanism is provided.

In the U-shaped magnetic field generator for MRI provided with a pair of magnet body structures 1 and 2 confronted at the interval of a void 8, a pair of magnet supporting yokes 2 provided outside the combination of the pair of magnet body structures and a main yoke 3 for linking the magnet supporting yokes to generate a magnetic field in the void inside the combination of the pair of magnet body structures, a sub yoke 9 is provided to be linked with the magnet supporting yokes within a range not to affect the magnetic field on the side where the main yoke is present with a surface parallel to the main yoke while including the center point of the magnetic field as a reference.