The National Institute of Information and Communications Technology (NICT) generated a real-time signal of an accurate time scale by combining an optical lattice clock and a hydrogen maser. The signal generated in this optical-microwave hybrid system continued for a half-year without interruption. The resultant one-second unit was more accurate than that of Coordinated Universal Time (UTC) on that date, and the time deviated by 0.8 nanoseconds in a half-year relative to TT(BIPM), where TT(BIPM) is the most accurate time scale post-processed by the International Bureau of Weights and Measures(BIPM). This demonstration proves the capability to keep time with respect to the future optical definition of the second, which may be realized in next 10 years. This achievement was published in an open-access journal Scientific Reports on March 9, 2018.