Huge amount of concrete is used for construction of infrastructures supporting our safety life. Recently, large number of concrete structures constructed during the high economic growth period are severely aged and deteriorated. Then, the development of adequate inspection methods and maintenance system are required. However, effective and accurate techniques which can be applied on site have not been established yet. Considering these backgrounds, our team focus on the chloride induced steel corrosion and propose the inspection method employing the near-infrared spectroscopy for measuring chloride content in PC grout at the unfilled PC sheath pipe, which will be very important for avoiding serious accidents. Moreover, a new technology using terahertz wave for inspection of surface quality of concrete and steel corrosion in concrete is investigated.