Abstract: 
Precision measurement of time and frequency has not only contributed to fundamental physics such as precision spectroscopy, test of constancy of fundamental constants and the theory of relativity, but has also played an important role as a core of social infrastructure such as synchronization of global positioning satellite systems and highspeed highcapacity networks. Time and frequency are defined by a cesium atomic clock based on microwave transitions, and its uncertainty reaches δν ⁄ ν_{0}≈10 ^{16}, making "second" a physical quantity that can be measured with outstanding precision in the SI unit system. On the other hand, with the invention of laser and the progress of coherent control technology of optical frequency such as optical frequency comb, the research of atomic clocks is shifting from microwave to optical clocks using electronic transitions in the optical domain. The optical lattice clock, proposed in 2001, is expected to be a nextgeneration timefrequency standard that can achieve both extremely high accuracy and stability by applying magic wavelength optical lattices, and an uncertainty of δν ⁄ ν_{0}≈10 ^{18}, two orders of magnitude better than that of the cesium clock, was achieved in 2016. Such a precise clock with an 18digit accuracy is capable of detecting gravitational redshifts corresponding to a height difference of 1 cm. The method of measuring elevation with clocks using relativistic time delays is called relativistic geodesy, and is attracting attention as a new geodetic technique. In this presentation, we will introduce our efforts to realize and improve the accuracy of optical lattice clocks and their application to relativistic geodesy.
