PURPOSE: To reduce the drift quantity of a static magnetic field due to a magnetic field of magnetic after effect and to improve the reproducibility of image quality by repeatedly applying a weak magnetic field tb a magnetic circuit during a stop period performing no imaging and reducing the magnetic after effect caused by a gradient magnetic field applied during an imaging period.

CONSTITUTION: In an MRI apparatus 100, a sequence memory circuit 8 operates a gradient magnetic field driving circuit 3 according to the command from a computer 7 to generate a gradient magnetic field in a magnet assembly 1 having an examinee received therein and also operates a gate modulation circuit 9 to modulate the signal of an RF oscillation circuit 10 and supplies the modulated signal to an RF power amplifier 4 to selectively excite an objective region. In this case, the sequence memory circuit 8 operates the gradient magnetic field driving circuit 3 on the basis of stored magnetic after effect reducing pulse sequence according to the command from the computer 7. A weak magnetic field is repeatedly generated from the gradient magnetic field coil of the magnet assembly 1. By this constitution, the magnetic after effect caused by the magnetic field applied during an imaging period is reduced.