<；P>；PROBLEM TO BE SOLVED: To easily improve airtightness and to efficiently reduce noise by suppressing the vibration of a cover. <；P>；SOLUTION: An airtight cover 12 has such an external shape as at least including a cylindrical section which has an external diameter smaller than the internal diameter of a first space formed inside a magnetostatic field magnet unit 1, at least the cylindrical section is disposed at a position in an end section side where the first space is opened, with respect to the disposal position of a gradient magnetic field coil unit 2 in the first space, to cover a region between the magnetostatic field magnet unit 1 and a bore tube 11 out of the opening. A vacuum seal 14 is disposed at a clearance between the inner circumferential face of the magnetostatic field magnet unit 1 and the cylindrical section to tightly seal the clearance. An O-ring 15 is disposed at a clearance between the bore tube 11 and the airtight cover 12 to tightly seal the clearance. <；P>；COPYRIGHT: (C)2011,JPO&INPIT
