Recently, railway companies are introducing energy-saving technologies, such as energy storage systems, energy-saving vehicles, and energy-saving driving operations. This results in the need for a method to accurately estimate the energy-saving effect of each technology. To this end, we developed a method to estimate of train operation energy consumption using the Train Operation Power Simulator. First, we developed a physical calculation algorithm of the Train Operation Power Simulator, unitizing the simultaneous measurements of substations and rolling stocks within a limited feeding section. Then, we developed an estimation method of commercial train operation energy consumption, unitizing the measurements of substations and commercial running data obtain from a train data collection device. We conclude that speed profile, running resistance, and auxiliary power of rolling stock are important for the energy consumption estimation. This study employs an algorithm of the speed profile generator for energy consumption estimation and a randomized braking method that adopts braking patterns derived from actual driving patterns obtained from commercial running data. In addition, this study employs the characteristics of running resistance obtained from running tests and the commercial running data, and the characteristics of auxiliary power obtained from commercial running data. © 2021 The Institute of Electrical Engineers of Japan.