A method includes collecting data for average units including acquisition of template data and acquisition of imaging data, calculating a frequency difference between a resonant frequency in a reference average unit and a resonant frequency of an object average unit based on a phase variation of the magnetic field in a period where the template data is collected in the reference average unit and a phase variation of the magnetic resonance signal in a period where the template data is collected in the object average unit, correcting a phase shift produced in image data collected in the object average unit constituted by one or more average units based on the frequency difference, and reconstructing an image concerning the subject based on the imaging data collected in the reference average unit and the corrected imaging data concerning the object average unit constituted by one or more average units.