The ultimate goal of the observational cosmology is to give answers to the fundamental questions, such as how the universe was born, how it evolved to show the present-day features, and what its fate is, on the basis of observational material. Research themes of the observational cosmology fall in two broad categories, the framework of the (uniform and isotropic) universe which is described by cosmological parameters and the (non-uniform) structure which is formed in it. Various issues in both categories should eventulally be understood in a consistent manner.

　We have been doing researches of observational cosmology based on observations at optical and near infrared wavelengths of galaxies and clusters of galaxies. Our research topics cover both the cosmological parameters (Hubble constant) and the structure formation (structure of galaxies and clusters of galaxies). We have been aiming to collect larger amount of data of better quality. In addition to using existing observational facilities, we have developed new instruments, facilities, and astronomical image data processing systems.

　We pay careful attention to the accuracy, especially, systematic errors, of the data and examine what the data really mean without making too much overinterpretation. Researches shown below are the results of collaboration with many colleagues including then graduate students.

* Sloan Digital Sky Survey (SDSS) is a wide-area survey project using dedicated telescopes and a large mosaic CCD camera which is being conducted by the international collaboration of United States, Japan, and Germany. The goal of the SDSS is to measure the brightness and position of approximately 100 million astronomical objects using the images of a quarter of the entire sky taken in five color bands and measure the distance of about 1 million bright galaxies and 100 thousands quasars from spectroscopic observations. The dedicated telescopes are located at Apache Point Observatory, New Mexico, United States. Participating institutions include the University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Max-Planck-Institute fur Atronomie, the Max-Planck-Institute fur Astrophysik, New Mexico State University, University of Pittsburgh, Princeton Unversity, the US Naval Observatory, and the University of Washington. Apache Point Observatory, site of the SDSS telescopes, is operated by the Astrophysical Research Consortium (ARC). Funding for the project has been provided by the Alfred P. Sloan Foundation, the SDSS member institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Sciety.