Nippon Telegraph and Telephone Corporation, in collaboration with the Tokyo Institute of Technology, the Japan Science and Technology Agency, and the Tohoku University, has successfully demonstrated an extremely sensitive ammeter, in which the flow of one electron in either direction can be detected in real time. The single-electron ammeter can be used to measure extremely small currents that cannot be measured with any existing meter and to analyze the motion of individual electron. It will be useful for studying nanoelectronics and developing quantum information technologies.