1. A magnetic resonance imaging apparatus comprising: a sensitivity map data generating unit configured to apply a first self correction processing for improving uniformity to non-uniform whole body coil data or non-uniform phased array coil data to generate reference image data, the non-uniform whole body coil data and the non-uniform phased array coil data being data acquired from an object using a whole body coil and a phased array coil, respectively, through a sensitivity map pre-scan, to apply a second self correction processing for further improving uniformity to the generated reference image data, after the first self correction processing, to generate corrected reference image data, the first self correction processing being rougher than the second self correction processing, to generate basic data for sensitivity map data using the corrected reference image data and the non-uniform phased array coil data, and to generate the sensitivity map data of the phased array coil from the basic data for the sensitivity map data; and a sensitivity corrected image data generating unit configured to acquire image data for imaging from the object with the phased array coil as a receive coil and to generate image data after sensitivity correction by performing the sensitivity correction of the image data using the sensitivity map data.