The fraction of blue galaxies in clusters is found to dramatically increase with redshift. This trend has been known as the Butcher-Oemler (B-O) effect which implies a significant evolution among the cluster galaxy population with time. It has been proposed that the blue galaxies in B-O clusters are at their last stage of star formation, probably using up the gas, which then might have evolved into red and passive cluster galaxies as found in the Local Universe. To test this hypothesis and ultimately to understand the evolution of cluster galaxy population as a function of redshift, we have embarked a multi-wavelength study of two carefully selected galaxy clusters at z~0.2 where the B-O effect becomes first noticeable. In this talk, I will introduce the Blind Ultra-deep Distant HI Environmental Survey (BUDHIES) on those two clusters and relevant multi-wavelength observations. Also, I will present the preliminary results of our recent Nobeyama CO observations of two galaxies selected among the BUHDIES sample.