To provide an MRI device capable of maintaining uniformity of a static magnetic field during imaging by effectively reducing induction current generated in a shim coil when driving a gradient magnetic field coil without having to grasp its magnitude.SOLUTION: An MRI device includes a static magnetic field generation device, a gradient magnetic field coil 30a for giving a magnetic field gradient to a static magnetic field generated by the static magnetic field generation device, and a shim coil 80a arranged close to the gradient magnetic field coil for correcting ununiformity of the static magnetic field. The MRI device further includes an additional circuit connected between the shim coil and a power source 81a in series for increasing a time constant of a circuit including the shim coil. The additional circuit is arranged so as to generate mutual inductance Mpositive to each other, and includes two additional coils 90 and 91, and these additional coils are arranged at a position where mutual inductance is not generated between the gradient magnetic field coil and the shim coil.SELECTED DRAWING: Figure 4【課題】傾斜磁場コイル駆動時にシムコイルに生じる誘導電流を、その大きさを把握する必要なく、効果的に低減し、撮影中の静磁場の均一度を維持するＭＲＩ装置を提供する。【解決手段】ＭＲＩ装置は、静磁場発生装置と、静磁場発生装置が発生する静磁場に磁場勾配を与える傾斜磁場コイル３０ａと、傾斜磁場コイルに近接して配置され、静磁場の不均一を補正するシムコイル８０ａと、を備え、シムコイルと電源８１ａとの間に直列に接続され、シムコイルを含む回路の時定数を増大する付加回路を備える。付加回路は、互いに正の相互インダクタンスＭＡＢを生じるように配置され２つの付加コイル９０、９１を有し、これら付加コイルが傾斜磁場コイル及びシムコイルとの間に相互インダクタンスを生じない位置に配置されている。【選択図】図４
