MRI magnet having shielding magnet

A magnetic field generator comprises a pair of plate yokes opposed to each other with a space in between. Each plate yoke has a main surface on which a permanent magnet is disposed. A shielding magnet is provided each at a forward portion on an open side and at a rearward portion, of another main surface in the plate yoke. A magnetic spacer is placed between the plate yoke and the shielding magnet. When assembling, a shielding magnet is mounted on a main surface of the spacer, and then another main surface of the spacer is placed on the main surface of the plate yoke. The shielding magnet is covered by a nonmagnetic cover member. A distance not smaller than 2 mm is provided between an outer surface of the cover member and a surface of the shielding magnet. The plate yoke is provided with nonmagnetic legs.