An MRI apparatus is provided in which a heat quantity penetrating into the helium tank of a superconducting magnet can be grasped to select a cryo-cooler to be incorporated, whereby consumption of liquid helium is suppressed and a static magnetic field is generated stably. The superconducting magnet includes a superconducting coil, containers 209 and 203 for accommodating the superconducting coil and a refrigerant, a cooler 208 for liquefy gas once again, the gas having been obtained by vaporizing the refrigerant in the containers, and a means for measuring the amount of vaporized refrigerant, while keeping the pressure in the containers at a constant level. The heat quantity penetrating into the containers and the coolability of the cooler are measured accurately, thereby enabling a combination in which the coolability of the cooler to be combined has capacity more than the heat penetration amount.