1. An image retrieval apparatus which retrieves an image similar to a predetermined query image from images to be retrieved by using an image feature vector, comprising: first image feature vector conversion means for receiving similarity computation image feature vector configuration information describing a configuration of an image feature vector for use in a similarity computation, and converting the image feature vector of the query image into a first image feature vector according to the similarity computation image feature vector configuration information; and second image feature vector conversion means for converting the image feature vector of the images to be retrieved into a second image feature vector according to the similarity computation image feature vector configuration information, wherein similarity between the first image feature vector and the second image feature vector is computed according to the similarity computation image feature vector configuration information.