I. Introduction
Recently, the deterioration of social infrastructures such as tunnels, bridges, and roads becomes a severe social problem. It is required to rapidly and adequately detect for abnormal parts of social infrastructures [1], [2]. The ground penetrating radar (GPR) is efficient for inspection of various social infrastructures. However, it is difficult to detect an underground object from a GPR image. Automatic detection systems of the underground object based on a machine learning and an artificial intelligence technique are required. Although detection methods by several neural networks have been investigated [3], [4], these previous methods cannot identify more information such as the material and the size of the underground object.