PURPOSE: To eliminate the deviation of images by impressing the superposed magnetic field to determine a tomographic plane only during the irradiation of a high-frequency pulse so that the band of the nuclear magnetic resonance signal at each tomographic plane is made the same.

CONSTITUTION: The current A1 of the superposed magnetic field SBO and the current B1 of the Z-axis ramp magnetic field are conducted in a period t1 at the timing for image formation. The 90° high-frequency pulse E1 is irradiated to an object to be detected after the specified value is attained. The currents A1, B1 are turned off and the currents C1, D1 of the X-axis and Y-axis ramp magnetic field are conducted in a period t2. The current A2 of the superposed magnetic field SBO and the current B2 of the Z-axis ramp magnetic field are conducted in a period t3 and the 180° high-frequency pulse E2 is irradiated to the above-mentioned object. The currents A2, B2 are turned off. The currents C2, D2 of the X-axis and Y-axis ramp magnetic fields are conducted and a nuclear magnetic resonance signal F is generated by making coincident the spin echoes from the period t4 and period t2 with each other. Since the superposed magnetic field SBO is irradiated only during the irradiation of the high-frequency pulse in the above-mentioned manner, the nuclear magnetic resonance signal having high S/N is thus obtd.