A 12CO (J = 2-1) observation of the quasar BR 1202-0725 at z = 4.7, in which a huge amount of molecular gas had been detected in the 12CO (J = 5-4) emission line, was made with the Nobeyama 45-m radio telescope. An upper limit of 1.2 mK in TMB (∼ 2.8 mJy) was obtained at a velocity resolution of 25 km s-1. The physical conditions of the molecular gas were examined using the CO emission-line ratios with the LVG model; the line ratios imply that the molecular gas is dense [n(H2) ∼ 103.5-5.5 cm-3] with a high kinetic temperature (50-100 K). The value of the CO-to-H2 conversion factor in this system is discussed and the molecular-gas mass is estimated to be less than 5.4 × 1011 M(Fisheye sign). Using these values, we tried to sketch the distribution of molecular gas in this system and find the possibility that the system consists of many small dense clouds.
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