1. An image information conversion method comprising the steps of: extracting, from facial image information of a plurality of one-dimensional different facial expressions of a predetermined human being, a plurality of facial expression components for each said facial expression corresponding to respective projective components for a plurality of coordinate axes on facial image representation space taking the entire face as a processing unit, calculating a plurality of synthesized facial components corresponding to facial image information of a synthesized facial expression at an arbitrary rate for specified arbitrary two of said different facial expressions by interpolation/extrapolation of a facial expression component corresponding to said two different facial expressions, and generating synthesized facial image information according to said plurality of synthesized facial expression components.