A magnetic field generator comprises a superconducting bulk body, which generates a superconducting magnetic field, a refrigerant vessel for storing solid nitrogen, a vacuum container, which accommodates therein the superconducting bulk body and the refrigerant vessel, and a refrigerator having a cooling head for cooling the refrigerant vessel. The superconducting bulk body is arranged along a wall of the vacuum container. The cooling head of the refrigerator and the refrigerant vessel are in thermal contact with each other. The refrigerant vessel and the superconducting bulk body are in thermal contact with each other.