A maintenance method for a magnetic resonance imaging apparatus comprising: a vacuum container evacuated in its inside; a liquid refrigerant container (303, 304) installed in the vacuum container to hold a liquid refrigerant therein; a superconducting coil (301, 302) installed inside the liquid refrigerant container to be rendered superconductive by being immersed in the liquid refrigerant and allowing current to flow therethrough; a cryo-cooler connected to an insertion port provided in the liquid refrigerant container to re-condense gas evaporated from the liquid refrigerant in the liquid refrigerant container, and an air flow-in preventing means (209, 216, 222, 224, 309) for raising the pressure in the liquid refrigerant container relative to the pressure outside the vacuum container, wherein the maintenance method comprises the steps of: raising the pressure in the liquid refrigerant container relative to the pressure outside the vacuum container by operating the air flow-in preventing means (209, 216, 222, 224, 309), monitoring the pressure in the liquid refrigerant container (303, 304) and in the room where the magnetic resonance imaging apparatus is installed, replacing the cryo-cooler after having raised the pressure in the liquid refrigerant container so that the raised pressure prevents air from flowing into the liquid refrigerant container from outside of the vacuum container via the insertion port, and ending the step of operating the air flow-in preventing means, after having replaced the cryo-cooler. a vacuum container evacuated in its inside; a liquid refrigerant container (303, 304) installed in the vacuum container to hold a liquid refrigerant therein; a superconducting coil (301, 302) installed inside the liquid refrigerant container to be rendered superconductive by being immersed in the liquid refrigerant and allowing current to flow therethrough; a cryo-cooler connected to an insertion port provided in the liquid refrigerant container to re-condense gas evaporated from the liquid refrigerant in the liquid refrigerant container, and an air flow-in preventing means (209, 216, 222, 224, 309) for raising the pressure in the liquid refrigerant container relative to the pressure outside the vacuum container, wherein the maintenance method comprises the steps of: raising the pressure in the liquid refrigerant container relative to the pressure outside the vacuum container by operating the air flow-in preventing means (209, 216, 222, 224, 309), monitoring the pressure in the liquid refrigerant container (303, 304) and in the room where the magnetic resonance imaging apparatus is installed, replacing the cryo-cooler after having raised the pressure in the liquid refrigerant container so that the raised pressure prevents air from flowing into the liquid refrigerant container from outside of the vacuum container via the insertion port, and ending the step of operating the air flow-in preventing means, after having replaced the cryo-cooler. raising the pressure in the liquid refrigerant container relative to the pressure outside the vacuum container by operating the air flow-in preventing means (209, 216, 222, 224, 309), monitoring the pressure in the liquid refrigerant container (303, 304) and in the room where the magnetic resonance imaging apparatus is installed, replacing the cryo-cooler after having raised the pressure in the liquid refrigerant container so that the raised pressure prevents air from flowing into the liquid refrigerant container from outside of the vacuum container via the insertion port, and ending the step of operating the air flow-in preventing means, after having replaced the cryo-cooler.