A magnetic field generator for MRI comprises a generator main body and a covering member for covering the whole generator main body, and the covering member is made of a non-magnetic material, for example a closely woven fabric of stainless steel, aluminum, copper, nylon, cotton, hemp, flax, rubber or plastics, and a fastening member is provided for fastening the covering member to the generator main body, which is formed of a string or a rope made of stainless steel, aluminum, copper, nylon, cotton, hemp, flax, rubber or plastics.