For the purpose of providing an MRI apparatus which gives rise to no phase deviation due to frequency alteration of the RF magnetic field and signals for detection use, the MRI apparatus includes: signal collecting means which detects and collects magnetic resonance signals generated by applying a magnetostatic field, a gradient magnetic field and an RF magnetic field onto an object; frequency altering means which alters the frequency of the RF magnetic field and the frequency of signals for detection use in accordance with change in the Larmor frequency with time; and image reconstructing means which reconstructs an image on the basis of the collected signals, and further comprises: phase control means which sets as the phase at the time of starting detection of signals for detection use a phase .DELTA..theta. given by a relational expression .DELTA..theta.=2.pi..DELTA.fT using the difference .DELTA.f between the frequency altered by the frequency altering means and a reference frequency, and a time period T from the start of applying the RF magnetic field to the start of detection of magnetic resonance signals.