We have three focal plane array receiver systems at 40, 100, and 150 GHz for the Nobeyama 45-m telescope. These array receivers cover the wide frequency range of Rayleigh-Jeans region of the Sunyaev-Zel'dovich (S-Z) effect. We have performed systematic observations the S-Z effect since 1997. From the pilot ON-OFF observations toward 8 X-ray bright galaxy clusters at 40 GHz, the Hubble constant was estimated to be H 0 = 64±17 km/s/Mpc for a flat Λ-CDM cosmology, which shows good agreement with

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... e values by other SZ effect observations. Mapping observations toward 6 galaxy clusters have been performed. The overall distribution of the hot plasma observed by S-Z effect roughly follow the spherical isothermal β-model, while there are some possible deviations from the model especially in the central core region.