The present invention provides an image information compressing apparatus of high coding efficiency with little deterioration in picture quality, capable of effectively extracting feature components from an image in an image information feature-extraction and coding method. An image information compressing apparatus 1 for performing feature extraction and coding on an original image includes a pseudo-Hilbert scanning means (5) for converting a two-dimensional or three-dimensional original image into one-dimensional original data by pseudo-Hilbert scan, a first feature information extracting means (6) for extracting first feature information by generating first feature data by approximating the one-dimensional original data by a predetermined function having redundancy larger than that of the one-dimensional original data, a first coding means (7) for coding the first feature information, thereby generating first feature coded data, a second feature information extracting means (8) for extracting second feature information by subtracting the first feature information from the original image, and a second coding means (9) for generating second feature coded data by coding the second feature information.