Two Way Satellite Time and Frequency Transfer (TWSTFT) is one of the most precise time transfer methods. Its developments and technical attempts for practical uses are under progress. This paper presents the research and development activities performed in CRL, such as development of multi-channel modems for TWSTFT and construction of the TWSTFT network in the Pacific Rim region. [キーワード] 時刻比較,衛星双方向時刻比較,国際原子時 Time transfer, Two way satellite time and frequency transfer, International atomic time