We are developing an optical lattice clock toward realization of the next-generation atomic clock. Optical clocks have an intrinsic superiority over the present Cs microwave clock, which is the definition of the SI second, because they can split time with a much higher rate. These ticks can be precisely counted by using an optical frequency comb, the inventors of which were awarded the Nobel Prize in 2005. The long remaining problem to search for the next-generation optical atomic clock can be solved by the revolutionary idea of the optical lattice clock proposed by Prof. Katori of the University of Tokyo in 2001. At AIST, we started developing the optical lattice clock using ytterbium atoms. This innovation will lead to the redefinition of the second in the near future.