1. An imaging apparatus, comprising: an imaging unit that captures an image by photoelectrically converting a subject image; a feature calculating unit that calculates, per each of plural regions included in the image, a feature value related to suitability for motion detection; a region-motion detecting unit that detects a motion vector per each of the regions; and a whole-motion calculating unit that calculates a motion quantity of a whole image from the feature values and the motion vectors, wherein the whole-motion calculating unit multiplies the motion vectors with a corresponding feature value that is related to the suitability for motion detection, and calculates a sum of the motion vectors that are multiplied with the corresponding feature value, and each feature value is an eigenvalue of a gradient covariance matrix of the region.