A magnetic field generator for MRI comprises a pair of plate yokes opposed to each other with space in between. A magnet is provided in each of the opposed surfaces of the pair of plate yokes. A column yoke is connected to the pair of plate yokes. An enhancing member made of magnetic material and having a curved slant face is provided in an inner surface of the connection between the column yoke and the plate yokes at a place farthest from the magnet. A first bolt of magnetic field adjusting bolts is screwed into the plate yoke, with a tip of the first bolt contacting the enhancing member. A second bolt of the magnetic field adjusting bolts is screwed into the plate yoke, with a tip of the second bolt contacting an upper end face of the column yoke. An engaging portion for engagement of the enhancing member with the yoke may be provided.