Abstract: A nuclear magnetic resonance imaging apparatus has a superconducting coil which generates a static magnetic field, an electrically-conducting tubular heat shield which surrounds the superconducting coil, and a pair of confronting circular coils which are coaxial with the longitudinal axis of the cylindrical thermal shield and generate a gradient field in the longitudinal direction of the heat shield. The magnetic field generated by the circular coils induces eddy currents in the heat shield, and the eddy currents generate magnetic fields which form a composite magnetic field together with the magnetic field generated by the circular coils. The circular coils are positioned such that the terms in the expression for the magnetic flux density of the composite magnetic field which are proportional to the cube of the distance in the longitudinal direction of thermal shield cancel one another.