We are developing radar technology to inspect the inner structure of wooden buildings suffered from strong quake by earthquake. GB-SAR (Ground Based Synthetic Aperture Radar) for inspection of wooden and concrete walls and structures has been developed and the system was evaluated by test measurements. The GB-SAR system uses frequency bandwidth 1-20GHz, and it can acquire full polarimetric radar signal. We found that frequency up to 20GHz can be usefully used for inspection, and show that the radar could achieve the resolution about 1.5cm, and found that t can be used for detection of crack inside concrete structure. Then Synthetic Aperture (SAR) Radar signal processing is used to reconstruct 3-dimenatioal images of inner structure of the targets. We found that the radar polarimetry gives us very precise information of the damaged structures, and demonstrated that radar polarimetry is a useful tool for detecting fractures inside a concrete structures, and detection of small deformation of wooden structures.