1. A nuclear magnetic resonance (NMR) imaging apparatus comprising: first imaging means for imaging a cross section of an object to be inspected according to a first imaging method of magnetic resonance integrated with a measurement operation and for reconstructing an image of said cross section; means for selecting a region of interest in the image of the cross section reconstructed by said first imaging means; coil means for establishing a gradient magnetic field; gradient magnetic field control means for controlling a gradient of the magnetic field to be larger at the selected region of interest than that at the other regions; and second imaging means for imaging the cross section of the object including said selected region of interest according to a second imaging method of a different class of imaging than that of the first imaging method when the gradient of the magnetic field is controlled by said gradient magnetic field control means and reconstructing an image thus obtained.