Degradation of aged power transmission system becomes a serious problem. As for a transmission tower inner corrosion of a steel pipe beam is one of issues because inspection from the external appearance of the pipe is difficult. In order to utilize practical inspection clarification of the corrosion properties of the pipe is required. In this study several atmospheric corrosion sensors (ACM sensors) were place at a regular interval inside the steel pipe which is set up at coastal testing field and time transition of corrosion behavior distribution inner steel pipe from end to center was evaluated. Following results were obtained with this experiment: (1) corrosion behavior inner steel pipe strongly depends on climate condition such as temperature relative humidity and weather (2) corrosion rate tends to become smaller from end to center direction of steel pipe (3) corrosion information acquired from ACM sensors is in good agreement with corrosion condition of steel pipe sample which concludes that the method used in this study is effective for the monitoring of corrosion inner of steel pipe.