1. A picture retrieving apparatus, comprising: a first orthogonal coefficient generating section which outputs a set of orthogonal coefficients of each of a plurality of pictures as a retrieval target picture; a second orthogonal coefficient generating section which outputs a set of orthogonal coefficients of a query picture; and an orthogonal transform coefficient similarity calculator which calculates a similarity between said set of orthogonal transform coefficients of said query picture and said set of orthogonal transform coefficient of said retrieval target picture.