1. A magnetic resonance imaging apparatus comprising a computer and associated storage unit configured to: set a plurality of inversion times different from each other for differentiating whether a tumor of an object is benign or malignant, each of the plurality of inversion times being an inversion time of a spin labeling pulse for tagging blood in a region to be tagged flowing into an imaging region of the object; and acquire a plurality of blood flow images respectively corresponding to the plurality of inversion times, without contrast medium, by applying the spin labeling pulse and an imaging sequence with each of the set plurality of inversion times.