Recently, as natural disasters like torrential rains and typhoons increase, loss of life and property damage have multiplied. But estimated damage amount for restoration is apt to be influenced by investigator`s subjective judgment because it is still manually calculated in the majority of cases. This makes accurate investigation for damage assessment difficult. Especially in 3D damage assessment, such as soil volume, the results vary widely with the investigators. In many cases, the damages are over estimated. We developed an estimating technique for 3D damage amount, which creates pre-disaster virtual surface using only post-disaster stereo images, and calculates the soil volume from the difference between pre-disaster virtual surface and post-disaster surface. The accuracy of developed technique was verified through Field Investigation System. The error was less than 6.4%.