A detailed excavation survey of the low temperature cracking area was conducted in Shiranuka, and it was confirmed that the surface of lower subbase course in the damaged area had turned black. This is because a part of the asphalt mixture breaks into fine-grained particles due to degradation, and the fine grains migrated and sedimented on the lower subbase course. It is thought that the asphalt stripped from the aggregate by the action of water as well. In this study, samples were picked from the surface of the subbase course, and asphalt content and its areal distribution was confirmed. Property tests were also conducted to evaluate the degree of oxidation degradation. In addition, the properties of the asphalt degradation were evaluated for all asphalt mixture courses according to the depth distribution, comparing with the properties of the sedimented asphalt on the subbase course.