1. A terrestrial object information interpreting image producing method for synthesizing radar image data of an area photographed by a radar device mounted on a flying body and optical image data of the area photographed by the radar device to produce a terrestrial object information interpreting image, the method comprising the steps of: approximating the radar image data to a black and white panchromatic image character; performing an alignment between the radar image data and the optical image data; and synthesizing the radar image data having been approximated to the black and white panchromatic image character and the optical image data.