Our key topic is “optical frequency comb”, in particular, fiber-based frequency combs which are the key for practical applications. By full use of its capability as an “optical synthesizer” in time, frequency, and space domains, we are developing a wide variety of application technologies. These include absolute length metrology with ultra-precision, ranging from picometer to killometer, and ultrabroad and rapid spectroscopy. These are applicable to industrial and environmental sensing, and space technology.