1. An image search device, comprising: a common memory; a plurality of parallel processors for executing a same instruction, reading data stored in the common memory in bulk, and processing the data; a storage means storing a plurality of image feature vectors that are respectively extracted from a plurality of images serving as search targets and respectively belong to one of a plurality of clusters, and a plurality of representative feature vectors each of which represents one of the plurality of clusters, in which more than one of the image feature vectors are extracted from one of the plurality of images; representative vector transfer means for transferring the plurality of the representative feature vectors from the storage means to the common memory; query feature vector obtaining means for obtaining and storing, in the common memory, one or more query feature vectors that are extracted from an image serving as a query; first distance calculating means for calculating a distance between at least a part of the plurality of transferred representative feature vectors and the query feature vector using the plurality of parallel processors; second distance calculating means for calculating a distance between the plurality of image feature vectors, which belong to the cluster selected based on a calculation result of the first distance calculating means, and the query feature vector; and selecting means for selecting at least one of the plurality of images based on a calculation result of the second distance calculating means.