Computer image processing technology has been applied to fracture surface analysis, and the generalized software for 3-dimensional fractography image analysis has been developed. By this software, it became possible to obtain 3-dimensional fracture surface topography from a stereo-pair of SEM fractograph with a sufficient precision. The fatigue fracture surface roughness of a hightensile strenght steel HT 55 in air and in vacuum was calculated, and the root mean square roughness of fracture surface in vacuum was made clear to be greater than that in air at R=-1, compared with those at R=0.1 and 0.5. The wedge effect induced by corrosion products was also clearly demonstrated on a matching-pair of corrosion-fatigue fracture surface topography of HT 55.