Comets are considered as the remnants of the planetesimals (building blocks of the planets) formed in the proto-planetary disk of the Sun. They have retained the information about the formation and evolutional history of the early solar system. To investigate the chemical and physical conditions of the proto-planetary disk, comets have been studied as probes to the solar system formation. In the last two decades, thanks to advances in technology, near-infrared (NIR) observations have been carried out to detect the various kinds of molecules (with and without permanent electric dipole moments) released directly from the nucleus. As the physical temperature could control chemical reactions, we expect to find chemical diversity among comets that have different dynamical origins. To investigate chemical diversity in the proto-planetary disk, we have observed several comets with NIR high-dispersion spectrometry. Although the number of samples is still small relative to the number of samples obtained by optical...